Plua 2.0

1. Introduction

Plua 2.0 requires PalmOS 3.5 or greater.

More information on Lua can be found here.
More information on Plua can be found here.
There is a Plua discussion group here (registration required).

THIS SOFTWARE COMES WITH ABSOLUTELY NO WARRANTY, SO USE IT AT YOUR OWN RISK.

Plua is Copyright (C) 2001-2006 Marcio Migueletto de Andrade.

2. Operation

For example, if you type in the text field this program:

print("Result = ", 2*3)

Result =   6

• The program is retrieved from a MemoPad record, a Doc file, a Stream file or a file stored in a VFS card.
• The entire screen is available to display results.

If you create Memo with Lua code, it must start with "-- " (without the quotes and with a trailing space) and then the program name (usually a single word) ended with ".lua", otherwise it will not be visible in Plua. Doc, Stream and VFS files must also end in ".lua".

Select one program on the list and tap the Run button to run it. Plua will switch to a full screen mode and run the program. When it is finished Plua will return to the program selection screen. If you want to stop a program before it is finished tap the Applications icon. Plua looks for VFS files in the /PALM/Programs/Plua/src directory on your expansion card.

The button Compile is used to compile a program into a PRC file. The generated PRC is a standalone application that can be accessed like any other one in the Application Launcher. Note however that Plua or PluaRT (the Plua runtime) needs to be installed. You do not need to install both if you just want to run Plua applications. If neither Plua nor the runtime is installed and a compiled program is run, an error message will be displayed and the program will be aborted. Generated PRCs have a fixed pre-defined icon. Note that it is not necessary to compile a program in order to run it. If you just to want to run a program from within Plua, you can use the Run button directly. The Compile button should be used only when you want to generate a standalone PRC with your program.

Tap the Main button to return to the main screen. For Memos you have two additional buttons: New and Edit, to create and edit Memos respectively. For Docs, there is also a Edit button. If you tap this button Plua will open the third-party application SrcEdit to edit your doc file. If this application is not installed nothing will happen.

Preferences are accessible via Menu/Preferences in the main screen. If "Read-only mode" is checked, all attempts to open a database for writing or removing a database will be aborted, and an error message will be displayed. If "Clear output" is checked, the Clear button also clears the output area.

The Plua online help system is accessible via the PalmOS standard "Find" button. If you tap Find while in the main window or editing a memo, Plua will open a dialog showing all function names. If you select one function name and tap Goto again Plua will show the function reference. If you tap the Index button, all function names will be shown again. Tap Done to close the help dialog. While in the main window or editing a memo, before tapping Find you may first select a word, in which case the help dialog will open directly in the function reference. In order to use the help system, you must first install pluahelp.prc.

3. Plua compared to Lua

• The following functions of the standard I/O library (liolib) are missing: os.difftime, os.execute, os.setlocale, io.popen. The os.date function is implemented partially (some formatting options are missing).
• There is no concept of "stdin", the standard input stream. Programs can read data from files, but not from user input. User input is restricted to pen/key events and interaction with UI components.
• The tonumber() function supports only base 10.
• Most of the functions in the standard mathematical library (lmathlib) require MathLib to work. MathLib is a third-party library and is not distributed with Plua.

Database I/O functions:

• os.listdb(creator, type [, suffix]): returns a table with all databases matching the specified type and creator, and optional suffix. Type and creator are either a 4 character string or an empty string to accept anything.
• io.open(name, mode): this is a standard Lua function, but in the case of PalmOS databases, besides the handle to the open file it returns the number of records in the database.
• f:getdbcat(n): returns the name of category n (where 0 <= n <= 15) from already open database f.
• f:setdbcat(n, "cat"): sets the name of category n (where 0 <= n <= 15) to "cat" on already open database f. Returns the category name just set.
• f:openrec(i): opens the record with index i from an already open database f. Returns the size of the record or nil if an error occurred.
• f:createrec(size): creates a new record with given size in (already open) database f. The record is added at the end of the database. The created record is NOT automatically opened, so it is necessary to call openrec() to open the just created record before using it. Returns the index of the new record or nil if an error ocurred.
• f:deleterec(i): deletes the record with index i from (already open) database f. The record can not be open when it is deleted. Returns true if success or nil if an error occurred.
• f:removerec(i): removes the record with index i from (already open) database f. The record can not be open when it is removed. Returns true if success or nil if an error occurred.
• f:closerec(): closes the current open record of (already open) database f. Returns true if success or nil if an error occurred.
• f:resizerec(i, size): resizes the record with index i from (already open) database f to the specified size. If the record beeing resized is the currently open record, it is closed, resized and then reopened. Returns true if success or nil if an error occurred.
• f:getreccat(i): returns the category number of record index i from already open database f.
• f:setreccat(i, n): sets the category number to n for record index i on already open database f. Returns the category number just set.
• f:getrecid(i): returns the unique ID of record index i from already open database f.

• f:status(): returns true if there is input pending on the serial or network connection f, or false otherwise. It can be used after receiving an ioPending event to know which connection has pending input.

• os.mkdir(name): creates a VFS directory. Returns true if success or nil if an error ocurred.
• os.listdir(name [, suffix]): returns a table with the file names in a VFS directory. If the optional parameter is specified only files with that suffix are returned.
• io.open(name): this is a standard Lua function, but it can be used to open a VFS directory for reading. Returns a handle to the open directory.
• f:readdir(): reads a directory entry. Returns the entry name and type (4=directory, 8=regular file, 10=link.

• resource.open("type", id [, file]): opens the resource with specified type (4 character string) and id. The resource is searched in all open databases or, if the optional file parameter is passed, only in the database named "file". Returns a number identifying the resource.
• resource.close(r): closes the resource identified by number r. The number r is returned by the resource.open() function. Returns nothing.
• resource.get(r [, start [, end]]): returns a string with the contents of the resource identified by number r. You can optionally specify just a substring of the resource, with the start and end parameters. The number r is returned by the resource.open() function. Returns a string with the resource.
• resource.size(r): returns the size of the resource identified by number r. If the resource is a bitmap, two additional numbers are returned: the width and the height of the bitmap. The number r is returned by the resource.open() function.
• resource.draw(r [, mode]): draws the bitmap resource identified by the number r in the current cursor position. The cursor is advanced to the right of the bitmap. The optional mode parameter affects how pixels are transfered to screen (0=paint, 1=erase, 2=mask, 3=invert, 4=overlay, 5=paint inverse). The number r is returned by the resource.open() function. If the resource is not a bitmap, this function has no efect. Returns nothing.

• screen.mode(): returns 4 numbers: screen width, screen height, screen depth and 1 or 0 indicating if the screen supports color. In interactive mode the screen height is half of the full-screen mode.
• screen.clear([c]): erases the screen with the background color or with the optional c color, and moves the cursor to 0,0. Returns nothing.
• screen.color(fg [,bg]): sets the foreground color (fg) and optionally the background color (bg). Returns nothing.
• screen.rgb(r, g, b): returns the color equivalent to the (Red,Green,Blue) components.
• screen.pos(): returns 2 numbers with the current x,y cursor position.
• screen.moveto(x [,y]): moves the screen cursor to the x,y position. If y is omited the current y position is used.
• screen.line(x1, y1, x2, y2 [,c]): draws a line from x1,y1 to x2,y2 using the fg color or the optional c color.
• screen.lineto(x, y [,c]): draws a line from current position to x,y using the fg color or the optional c color.
• screen.set(x, y [,c]): draws a pixel at position x,y using the fg color or the optional c color.
• screen.get(x, y): return a number with the color of pixel at position x,y.
• screen.rect(x, y, dx, dy [,c]): draws a rectangle at x,y, extending dx,dy pixels, using the fg color or the optional c color.
• screen.box(x, y, dx, dy [,c]): draws a filled rectangle at x,y, extending dx,dy pixels, using the fg color or the optional c color.
• screen.circle(x, y, rx, ry [,c]): draws an ellipse centered at x,y, with rx,ry as x,y radius, using the fg color or the optional c color. Use rx=ry for a circle.
• screen.disc(x, y, rx, ry [,c]): draws a filled ellipse centered at x,y, with rx,ry as x,y radius, using the fg color or the optional c color. Use rx=ry for a filled circle.
• screen.fill(x, y, [,c]): starts a flood fill in the pixel located at x,y with current color or the optional c color. The filling stops at pixels with a different color than the initial pixel. Returns nothing.
• screen.font(f): sets the text font to number f. Returns two numbers with the "average" width of a character and the height of a character, both in pixels. Note that PalmOS fonts are not fixed-width fonts, so if the returned width is used in calculations, you get just an approximation.
• screen.textsize(text): returns the width and height of the text string in pixels.
• screen.clip(x, y, dx, dy): sets the clipping region to the rectangle at x,y, extending dx,dy pixels. If no parameter is passed the clipping region is reset. Returns nothing.
• screen.heading(r): sets the turtle heading to r radians. 0 points to the right, math.pi/2 points up, and so on. Returns nothing.
• screen.turn(r): turns the turtle r radians. r can be positive or negative and it is added to the current heading. Returns nothing.
• screen.walk(d): draws a line from the current cursor position, with extent d pixels and following the current heading. The cursor is positioned at the end of the line. Returns nothing.
• screen.jump(d): moves the cursor d pixels from the current cursor position, following the current heading. Returns nothing.

• buffer.get(x, y, dx, dy): saves in a buffer the pixels delimited by a rectangle at x,y, extending dx,dy pixels. Returns a number identifying the saved buffer.
• buffer.new(dx, dy): creates an blank buffer extending dx,dy pixels. Returns a number identifying the new buffer.
• buffer.put(id, x, y [,mode]): draws a saved buffer at coordinates x,y. The optional mode parameter affects how pixels are transfered (0=paint, 1=erase, 2=mask, 3=invert, 4=overlay, 5=paint inverse). Returns nothing.
• buffer.use([id]): sets a selected buffer for drawing. If the argument is missing, the screen is selected for drawing. Returns nothing.
• buffer.free(id): frees the saved buffer. Returns nothing.
• buffer.write(filename [,id]): writes buffer identified by id into file filename. If id is not specified the current screen is written. Returns the resulting file size or nil in case of error.
• buffer.read(filename): reads a buffer from file filename. Returns a number identifying the new buffer, its width and its height. In case of error, nil is returned.

• sprite.init(buffer [,x, y]): initializes the sprite engine. It must be called before any other sprite method. It accepts as argument a buffer handle created by buffer.new or buffer.read. This buffer will be used as the static background during the animation. Two additional optional parameters are the horizontal and vertical coordinates of the background top left corner on the screen (the background does not need to be the same size of the screen). Returns true on success, or nil plus an error message.
• sprite.finish(): finishes the sprite engine. Calling any other sprite method after finish is an error. Returns true on success, or nil plus an error message.
• sprite.add(index, table): adds one sprite to the sprite engine. At most 32 simultaneous sprites are supported. The first argument is the sprite index, between 1 and 32. This number is also the sprite priority. Lower numbered sprites are draw "below" higher numbered sprites. The second argument is the sprite definition table. Sprites can be added and removed between calls to sprite.update(). Returns true on success, or nil plus an error message.
• sprite.remove(index): removes one sprite from the sprite engine. The single argument is the sprite index. Sprites can be added and removed between calls to sprite.update(). Returns true on success, or nil plus an error message.
• sprite.update(): draws a complete frame to the screen, with background and all active sprites. The collision callback functions (if any) are also called inside the update method. To perform smooth animation, you will have to intercalate calls to gui.event (with the timeout parameter) and sprite.update.

• gui.title([text]): sets the title of the current form. Works only in full-screen mode. If the parameter is omited, the title is erased.
• gui.menu(t): defines the menu items. Currently there is one fixed menu item that is always available: "About Plua". It is possible to define additional items by passing a table with strings to gui.menu(). If a string starts with a letter followed by a colon, the letter is used as the item's shortcut.
• gui.label(text): creates a label with given text in the current cursor position. The cursor is positioned to the right of the component. Returns the ID of the component or nil if it could not be created.
• gui.button(text [,bmpId]): creates a button with given text in the current cursor position. The cursor is positioned to the right of the component. If the optional bmpId is passed and the PalmOS version supports graphic controls, a graphic button with the given bitmap resource ID is created instead. Returns the ID of the component or nil if it could not be created.
• gui.pbutton(text [,g [, bmpId]]): creates a pushbutton with given text in the current cursor position. Pushbutons can be optionally placed in a given group number g. The cursor is positioned to the right of the component. If the optional bmpId is passed and the PalmOS version supports graphic controls, a graphic button with the given bitmap resource ID is created instead. Returns the ID of the component or nil if it could not be created.
• gui.rbutton(text [,bmpId]): creates a repeating button with given text in the current cursor position. The cursor is positioned to the right of the component. If the optional bmpId is passed and the PalmOS version supports graphic controls, a graphic button with the given bitmap resource ID is created instead. Returns the ID of the component or nil if it could not be created.
• gui.checkbox(text): creates a checkbox with given text in the current cursor position. The cursor is positioned to the right of the component. Returns the ID of the component or nil if it could not be created.
• gui.selector(text [,bmpId]): creates a selector trigger with given text in the current cursor position. The cursor is positioned to the right of the component. If the optional bmpId is passed and the PalmOS version supports graphic controls, a graphic button with the given bitmap resource ID is created instead. Returns the ID of the component or nil if it could not be created.
• gui.slider(width, range [,value]): creates a slider control with the specified width in pixels. The slider values go from 0 to range-1. The optional value parameter is the initial slider value. The cursor is positioned to the right of the component. Returns the ID of the component or nil if it could not be created.
• gui.field(lines, cols, max [,text [, e, u]]): creates a text field with given number of lines and columns in the current cursor position. The field will accpet at most max chars. The field is optionally initialized with the specified text. The optional parameter "e" and "u" are values indicating if the field is editable and underlined, respectively. A nil value means false, and not nil value means true. If these parameters are passed, the text parameter must also be passed. The cursor is positioned below the component. Returns the ID of the component or nil if it could not be created. For fields with more than 1 line, a scroll bar is automatically placed to the right of the field if the user enters more text than the number of lines can display.
• gui.fieldattr(id, e, u): sets the attributes of an existing field identified by the given ID. The next two parameters are the same as in pfield(). Returns nothing.
• gui.setfocus(id): sets the focus to the field identified by the given ID. Works only with text fields. Returns nothing.
• gui.list(lines, cols, t [,sel]): creates a list with given number of lines and columns in the current cursor position. The list is filled with the elements of table t. Optionally the selected element is set to index sel. The cursor is positioned to the right of the component. Returns the ID of the component or nil if it could not be created.
• gui.popup(t [,sel]): creates a popup list in the current cursor position. The list is filled with the elements of table t. The size is automatically adjusted. Optionally the selected element is set to index sel. The cursor is positioned to the right of the component. Returns the ID of the component or nil if it could not be created.
• gui.gettext(id): returns a string with the text of the component identified by the given ID. For labels, buttons, pushbuttons, repeating buttons and checkboxes, the text is the label of the component. For field, the the text is its current contents. For list, the text is the current selected element.
• gui.settext(id, text): sets the text of the component identified by the given ID. Works with buttons, pushbuttons, repeating buttons, checkboxes, labels, fields and lists. For labels, the text is changed only if the new length is not greater than the current length. For lists, the text argument must be a table. Returns nothing.
• gui.inserttext(id, text): inserts a string text in the field identified by the given ID. Returns nothing.
• gui.getstate(id): returns a number with the state of the component identified by the given ID. For pushbuttons and checkboxes, the number is 1 if selected, 0 if not selected. For lists and popups, the number is the index of the selected item. For fiels, two numbers are returned: the start and ending position of the selected text.
• gui.setstate(id, n): sets the state (or index for lists and popups) of the component identified by the given ID. Works with pushbuttons, checkboxes lists and popups. Returns nothing.
• gui.setstate(id, start [,end]): if only start is passed, sets the insertion point of the field identified by the given ID. If end is also passed, selects a portion of the field text (from start to end). Returns nothing.
• gui.nl(): positions the cursor at (x,y), where x is the leftmost position and y is below the "tallest" component of the current "line". Returns nothing.
• gui.tab([n]): advances the cursor 8 pixels to the right. It is useful when separating UI components on the same line. If n is specified the cursor is advanced 8*n pixels. Returns nothing.
• gui.destroy(): destroys all UI components currently in the screen. Returns nothing.
• gui.alert(text): opens a information dialog with specified text. The user must press the Ok button to close the dialog. Returns nothing.
• gui.confirm(text): opens a confirmation dialog with specified text. The user must press either the Yes or the No button to close the dialog. Returns 1 if Yes was pressed or nil if No was pressed.
• gui.input([text [,initial]]): opens an input dialog with an optional text as title. A second optional parameter defines the initial value of the input. The user can enter up to 255 characters of input. The user must press either the Ok or the Cancel button to close the dialog. Returns a string with the input entered if Ok was pressed, or nil if Cancel was pressed.
• gui.selectdate([text [, y, m, d]]): opens the PalmOS day selection dialog. Text is an optional title, and y/m/d are the year, month and day initially shown in the dialog. Returns three numbers with the selected year, month and day, in this order, or nil if Cancel was pressed.
• gui.selecttime([text [, h, m]]): opens the PalmOS time selection dialog. Text is an optional title, and h and m are the hour and minute initially shown in the dialog. Returns two numbers with the selected hour and minute, in this order, or nil if Cancel was pressed.
• gui.selectcolor(text, c): opens the PalmOS color selection dialog. Text is the dialog title, and c is the initial color shown in the dialog. Works only in full screen mode, and only on PalmOS 3.5 or greater. Returns a number with the selected color if Ok was pressed, or nil if Cancel was pressed.
• gui.gsi(): creates a Graffiti State Indicator in the current cursor position. Works only in full screen mode, and only on PalmOS 3.5 or greater. Returns nothing.
• gui.dialog(x, y, dx, dy, title): pops up an empty dialog at position x,y with dimensions dx,dy. Controls can be created inside the dialog. The dialog must be closed with gui.destroy.
• gui.event([n]): blocks until an event is generated. Events can be a hard button press, a pen event, a UI control selection or whether there is I/O pending. The first returned value is always the event type: penDown, penUp, penMove, keyDown, ctlSelect, ctlRepeat, popSelect, lstSelect, menuSelect, ioPending, sampleStop, appStop or nilEvent (these constants are pre-defined). The ioPending event is a efficient way for a program to wait for I/O without polling. The appStop event is sent when the user quits the application. The only way to exit a running application is to catch this event end quit the event loop. If the optional n parameter is passed, gui.event() will wait at most n millisecons for an event. If no event happens, it will return nilEvent.
• gui.control(table): creates a label, button, pushbutton, repeating button, selector trigger, slider, field, list or popup with custom attributes defined in the table parameter. Returns the ID of the component or nil if it could not be created.

• sound.beep(n): plays the system sound identified by the number n. Returns nothing.
• sound.tone(freq, len [,volume]): plays a tone with frequency freq (in Hz), duration len (in millisenconds), and optionally volume (0-64). Returns nothing.
• sound.play(filename [,slot, volume]): plays sampled sound stored in a WAV file. The WAV file can be a VFS file, a stream file, or a resource. Slot is a number from 1 to 3, allowing up to three simultaneous sampled sounds. If slot is not specified the default value is 1. If volume (0-64) is not specified, the default system Game volume is used. Returns the duration of the sampled sound in seconds, or nil in case of error. After the sample is played a sampleStop event is generated.
• sound.stop([slot]): stops playing a sampled sound. If slot is not specified the default value is 1. Returns nothing.

• bit.andb(n1, n2): returns a bitwise AND between integers n1 and n2.
• bit.orb(n1, n2): returns a bitwise OR between integers n1 and n2.
• bit.xorb(n1, n2): returns a bitwise XOR between integers n1 and n2.
• bit.notb(n): returns a bitwise NOT of integer n.

• bin.pack("format", data): packs the elements of table data into a binary string, and the returns this string. The binary data format is specificed by the string argument format, in which each letter refers to a different encoding: B=8 bits unsigned integer; W=big endian 16 bits unsigned integer; L=big endian 32 bits unsigned integer; F=big endian 32 bits float; D=big endian 64 bits double; S=variable length string, ended with ASCII null.
• bin.unpack("format", string): unpacks a binary string encoded with pack() and returns a table with the decoded elements.

• os.getprefs("creator", id): returns a string with the preferecences specified by creator and id, or nil if it does not exist.
• os.setprefs("creator", id, prefs): sets the preferecences specified by creator and id to the given string prefs. Returns nothing.
• os.sleep(s): pauses the execution for s seconds (s can be a decimal number). Returns nothing.
• os.copy(s): copies the string s to the clipboard. Returns nothing.
• os.paste(): returns a string with the contents of the clipboard.
• os.mem(): returns used memory and total memory, both in KB.

• _VERSION: a string with the Lua version number (this is a standard Lua feature).
• _PLUA_VERSION: a string with the Plua version number.
• _OS_VERSION: a string with the PalmOS version number.
• _OS_NAME: a string with the OS name.

4. A small tutorial

• Comments start with -- and extend to the end of line.
• Statements are not ended by ";"
• Variables do not need to be declared.
• Variables are not typed, but values are. Values can be numbers, strings, functions or tables. Values are automatically converted to the right type when possible. For example, the code 1+"2" evaluates to 3.
• String concatenation is done with the .. operator. For example, the code "abc".."def" evaluates to "abcdef".
• Multiple assignments are supported. For example, the code x,y=2,3,4 assigns 2 to x and 3 to y. Non-used values are discarded (like 4 above).
• Functions can return multiple values. For example, if function f return 2 values, they can be retrieved using x,y=f()
• You can print a list of expressions using the function print: print(123,"abc",4*5,sin(45))

4.1. The display

The statement

screen.line(0,0,19,19)

write("abc")

Besides the cursor position, Plua also stores the current foregroung color, the current background color and the current font. The following example writes the string "Plua" in red over black with the bold font:

screen.color(screen.rgb(255,0,0), screen.rgb(0,0,0))
screen.font(1) print("Plua")

width, height, depth, hasColor = screen.mode()
print(width, height, depth, hasColor)

red = screen.rgb(255,0,0)
print(red)

screen.clear() w,h = screen.mode() screen.moveto(w/2,h/2)
for d = 1,20,1 do
  screen.walk(d) screen.turn(math.rad(-40))
end

4.2. Bitmaps

4.2.1. Using Windows BMP format

• The bitmap can not be compressed.
• The bitmap depth must be 1, 4, 8 or 24 bits (16 bits is not supported).
• After the bitmap is read, it is internally converted to 8 bits, even if the display supports a higher depth.

Store the file on a memory card

Using a memory card reader, copy "picture.bmp" to some directory on the memory card, for example "/data/picture.bmp". Then your application can use a code like this to open and display the bitmap:

bmp,bmp_width,bmp_height = buffer.read("vfs0:/data/picture.bmp")
width,height = screen.mode()
buffer.put(bmp, (width-bmp_width)/2, (height-bmp_height)/2)
buffer.free(bmp)

Store the file on a stream file

Using a memory card reader, copy "picture.bmp" to some directory on the memory card, for example "/data/picture.bmp". Then you need to copy the bitmap from the memory card to a stream file (you need to do this only once). In this example, the stream file is named "Picture":

bmp = buffer.read("vfs0:/data/picture.bmp")
buffer.write("Picture", bmp)
buffer.free(bmp)

bmp,bmp_width,bmp_height = buffer.read("Picture")
width,height = screen.mode()
buffer.put(bmp, (width-bmp_width)/2, (height-bmp_height)/2)
buffer.free(bmp)

Store the file on a resource

This method stores the BMP file in the same PRC file of your application. You must use the Plua desktop compiler to compile your application. This method works only if the Windows bitmap does not exceed 64K.

On your desktop development environment, copy the "picture.bmp" file to a file named "Wbmp03d0.bin" ("Wbmp" is just an arbitrary resource type, 03d0 is 2000 in hexadecimal, which is the ID we chose for the bitmap resource). You must compile your application using a syntax like this:

plua2c -name MyApp -cid MyCr -o MyApp.prc MyApp.lua Wbmp03d0.bin

bmp,bmp_width,bmp_height = buffer.read("rsrc:/Wbmp/2000")
width,height = screen.mode()
buffer.put(bmp, (width-bmp_width)/2, (height-bmp_height)/2)
buffer.free(bmp)

4.2.2. Using PalmOS Bitmap format

BITMAPFAMILYEX ID 2000
BEGIN
  BITMAP "Picture.bmp" BPP 8 DENSITY 144
END

pilrc Picture.rcp

plua2c -name MyApp -cid MyCr -o MyApp.prc MyApp.lua Tbmp03d0.bin

bmp = resource.open("Tbmp", 2000)
bmp_size, bmp_width, bmp_height = resource.size(bmp)
width,height = screen.mode()
screen.moveto((width-bmp_width)/2, (height-bmp_height)/2)
resource.draw(bmp)
resource.close(bmp)

4.3. Sprites

The sprite definition table has five mandatory fields:

• x: the sprite x coordinate in pixels.
• y: the sprite y coordinate in pixels.
• bitmap: the sprite bitmap handle (you get it with resource.open). Bitmap transparency is supported and handled automatically.
• active: a boolean flag, telling if sprite is active. An inactive sprite is not shown during the animation.
• collision: a Lua function that is called when the sprite collides with another one. The function is called with two arguments: the sprite definition tables of the two sprites that collided. If you do not want collision detection for a sprite, do not set its collision field.

Fields x and y must be updated by your program to move the sprite. Coordinates are relative to the background buffer. The bitmap field is usually set only once at the beginning, but can also be updated during the animation to change the sprite appearance. Since the sprite definition table is a regular Lua table, you can use it to store other fields belonging to your program logic.

4.4. User Interface

textField = gui.field(1,20,20)
lengthButton = gui.button("Length") gui.nl()
while true do
  ev,id = gui.event()
  if ev == ctlSelect and id == lengthButton then
    print(string.len(gui.gettext(textField)))
  elseif ev == appStop then
    break
  end
end

NOTE: since this program enters an infinite loop, the only way to stop it is to catch the appStop event and drop out of the loop.

The example below shows gui.input(), gui.alert() and gui.confirm().

s = gui.input("Write something")
if s ~= nil then
  gui.alert("You wrote "..s)
end

if gui.confirm("Are you tired ?") then
  print("Me too")
else
  print("Me neither")
end

gui.menu{"O:Open", "Preferences", "-", "Q:Quit"}

When one of the menu items is selected (except the About item), a menuSelect event is returned by gui.event(). In the example above, if "Preferences" was selected, gui.event() would return menuSelect and the number 2, meaning that the second user defined item was selected.

The following table shows all events returned by gui.event(). The general syntax is:

  event,arg1,arg2 = gui.event(timeout)

The following table lists the fields used to create GUI controls with the gui.control() function. This single function can be used to create controls that would be created with gui.label, gui.button, gui.pbutton, gui.rbutton, gui.checkbox, gui.selector, gui.slider, gui.field, gui.list and gui.popup.

The gui.control() function expects a a table as its single argument. The table has a mandatory field named "type", and its value must be one of the values listed in the first column on the table above. Other fields are optional, and have default values as defined above. For example, these two forms are equivalent:

gui.button("OK")
gui.control{type="button", text="OK"}

gui.control{type="button", text="OK", width=30}

4.5. File I/O

Regular files are implemented using the File Stream API of PalmOS, so Lua programs can open, create, read from and write to files normaly, without knowing about database types or database creators. The following example shows this:

f = io.open("MyOutput", "w")
f:write("This is being written to a PalmOS stream database")
f:close()

f,n = io.open("db:/MemoDB", "r")
for i = 0,n-1,1 do
  f:openrec(i)
  s = f:read("*l")
  print(s)
end
f:close()

Listed below are the modes available for opening files with io.open().

• "r": open for reading.
• "r+": open/create for reading/writing. If the file exists it is preserved, if the file does not exist it is created.
• "w": open/create for writing. If the file exists it is truncated, if the file does not exist it is created.
• "a": open/create for writing. If the file exists it is preserved and the file pointer is positioned at the end, if the file does not exist it is created.

Besides streams and databases, Plua also supports access to other I/O facilities, like resources, VFS files, TCP/IP sockets, or any device accessible by the PalmOS New Serial Manager. The following table shows all supported file types, the io.open() syntax and wether each mode is supported.

The standard dofile() function works with Doc files, MemoPad records and compiled applications. If there is a Doc file named "name.lua", for example, it can be included by using dofile("name.lua"). For MemoPad records, the record name must be prefixed with the string "memo:". If there is a record named "-- name.lua", for example, it can be included by using dofile("memo:/name.lua"). For applications, the compiled lua code can be included by using dofile("appname"), where "appname" is the PRC name.

A note about error handling in file I/O: in case of success, the functions marked as returning true in fact return an userdata value (which is true, since any non-nil value is considered true in Lua). The value of this userdata is not important, it is used just to make it different from false (nil). In case of failure, all I/O functions (except for read) return two additional values besides nil. The second value is a string with the error message and the third value is the numeric error code. The error messages/codes are inspired on the Unix C Library (libc) errors. Currently the following errors may be reported:

• ENOENT: No such file or directory
• EIO: Input/output error
• EBADF: Bad file descriptor
• ENOMEM: Cannot allocate memory
• EACCES: Permission denied
• EBUSY: Device busy
• EEXIST: File exists
• ENODEV: Operation not supported by device
• EINVAL: Invalid argument
• EMFILE: Too many open files
• EFBIG: File too large
• ENOTDIR: Not a directory
• EISDIR: Is a directory
• ENOSPC: No space left on device
• ENETDOWN: Network is down
• ENOTCONN: Socket is not connected
• EMSGSIZE: Message too long
• EINPROGRESS: Operation now in progress
• ENXIO: Device not configured
• EOPNOTSUPP: Operation not supported
• EADDRINUSE: Address already in use
• ETIMEDOUT: Operation timed out
• EISCONN: Socket is already connected
• ECONNRESET: Connection reset by peer
• ESOCKTNOSUPPORT: Socket type not supported
• EPROTONOSUPPORT: Protocol not supported
• ENETUNREACH: Network is unreachable
• EWOULDBLOCK: Operation would block
• EALREADY: Operation already in progress
• EADDRNOTAVAIL: Can't assign requested address
• ECONNREFUSED: Connection refused
• EHOSTUNREACH: No route to host

f,n,e = io.open("db:/Test", "r")

The following example shows how to open the serial port and wait for data in a efficient way.

f = io.open("srm:/serial/57600/8N1")
while true do
  ev = gui.event()
  if ev == ioPending then
    s = f:read(8)
    print(s)
  elseif ev == appStop then
    break
  end
end
f:close()

4.6. Binary data

Storing a a table into a PDB record:

table = {25, "Plua", 3.1416, 9999}
data = bin.pack("BSDW", table)
f = io.open("db:/MyBinaryData", "w")
index = f:createrec(string.len(data))
f:openrec(index)
f:write(data)
f:close()

According to the format string "BSDW", the number 25 (the first element) is packed as a byte, the string "Plua" is packed as a null-terminated string, the number 3.1416 is packed as a double and the number 9999 is packed as a 16 bit word. The returned data is a binary string of 1+5+8+2 = 16 bytes. This data is stored as record in the MyBinaryData PDB.

Reading the same record into a table:

f = io.open("db:/MyBinaryData", "r")
f:openrec(index)
data = f:read("*a")
table = bin.unpack("BSDW", data)
f:close()

After this, the returned table will have the same elements as the original one.

4.7. Libraries

For a description on how to build C libraries and integrate them into Plua, please look at the libkit examples.