;; Example 6-1 Blending Example (use gl) (use gl.glut) (define *left-first* #t) (define (init) (gl-enable GL_BLEND) (gl-blend-func GL_SRC_ALPHA GL_ONE_MINUS_SRC_ALPHA) (gl-shade-model GL_FLAT) (gl-clear-color 0.0 0.0 0.0 0.0) ) (define (draw-left-triangle) (gl-begin GL_TRIANGLES) (gl-color '#f32(1.0 1.0 0.0 0.75)) (gl-vertex '#f32(0.1 0.9 0.0)) (gl-vertex '#f32(0.1 0.1 0.0)) (gl-vertex '#f32(0.7 0.5 0.0)) (gl-end)) (define (draw-right-triangle) (gl-begin GL_TRIANGLES) (gl-color '#f32(0.0 1.0 1.0 0.75)) (gl-vertex '#f32(0.9 0.9 0.0)) (gl-vertex '#f32(0.3 0.5 0.0)) (gl-vertex '#f32(0.9 0.1 0.0)) (gl-end)) (define (disp) (gl-clear GL_COLOR_BUFFER_BIT) (if *left-first* (begin (draw-left-triangle) (draw-right-triangle)) (begin (draw-right-triangle) (draw-left-triangle))) (gl-flush) ) (define (reshape w h) (gl-viewport 0 0 w h) (gl-matrix-mode GL_PROJECTION) (gl-load-identity) (if (<= w h) (glu-ortho-2d 0.0 1.0 0.0 (* 1.0 (/ h w))) (glu-ortho-2d 0.0 (* 1.0 (/ w h)) 0.0 1.0)) ) (define (keyboard key x y) (cond ((or (= key (char->integer #\t)) (= key (char->integer #\T))) (set! *left-first* (not *left-first*)) (glut-post-redisplay)) ((= key (char->integer #\escape)) (exit 0)) )) (define (main args) (glut-init args) (glut-init-display-mode (logior GLUT_SINGLE GLUT_RGB)) (glut-init-window-size 200 200) (glut-create-window *program-name*) (init) (glut-reshape-func reshape) (glut-keyboard-func keyboard) (glut-display-func disp) (glut-main-loop) 0)