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12 Simple Closures

This chapter documents module (sdl simple).

This module provides some simple abstractions to introduce common Guile-SDL programming idioms. Although the interfaces are documented, they are permanently alpha, that is, subject to change w/o notice. Instead of relying on the stability of the interface, you are encouraged to look at the implementation as a model for creating customized abstractions.

Procedure: simple-canvas init? w h bpp [flags…]

Return a canvas closure that accepts a few simple messages. If init? is non-#f, initalize the SDL video subsystem first. w, h, and bpp specify the width, height, and bits-per-pixel, respectively. flags are symbols to set the video mode. If omitted, the default is hw-surface and doublebuf.

The closure, if called without arguments, returns the video surface. Otherwise, the following messages are recognized:


Return a rectangle the width and height of the canvas.

#:set-bg! r g b

Set the background color (used for clearing) to the color specified by r, g and b (integers 0-255), respectively. By default it is black (all values zero).


Fill the canvas with the background color.


Return width, height, or a cons of width and height, respectively.

#:resize! new-width new-height

Request that the canvas dimension be changed to new-width by new-height. Return a rect that reflects the actual dimension.

Procedure: simple-stylus init? filename size r g b

Return a stylus closure that accepts a few simple messages. If init? is non-#f, initialize the SDL TTF support first. filename specifes the .ttf file to load and size the size. r, g and b are integers (0-255) specifying the color. The closure recognizes the following messages:

#:set-font! filename size
#:set-color! r g b

Change the font or color, respectively.

#:set-canvas! surface

Set the surface on which the #:write! command renders.

#:render text [color [bg]]

Return a surface of text rendered using the default font, size, color and size. Optional second arg color specifies another color to use. Optional third arg bg specifies a background mode: #f (default) for “solid”; #t for “blended”; a color to use that color.

#:write! where text [color [bg]]

Similar to #:render, but also blit the surface onto the canvas at the rectangle position specified by where. The width and height components of where are updated by side effect.

Procedure: simple-vpacked-image filename [canvas]

Return a vpacked image closure that accepts a few simple messages. "Vpacked" means multiple vertically-abutted images of dimensions NxN (at the top) through Nx1 (at the bottom), stored in a single image file. filename specifies the file and optional arg canvas specifies a surface for blitting. The closure recognizes the following messages:

#:set-canvas! surface

Change the canvas.


Return the vector of rectangles of length N+1 (the element at index zero is #f) corresponding to areas on the image representing the smaller sub-images. The element at index I is a rectangle of dimension IxI.

#:blit! i rect

Blit the sub-image i (an integer 1 <= I <= N), onto the canvas. rect specifies a rectangle to blit to.

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