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;; Extremely simply OpenGL demo.
;; Draw a shaded rectangle on the screen.
;; Also query some information on the OpenGL implementation.
#lang racket/gui
(require (planet "rgl.rkt" ("stephanh" "RacketGL.plt" 1 4)))
(require ffi/vector)
(require "viewer.rkt")
(define texture #f)
(define (setup)
;; Note that we can only load textures once we have an OpenGL context!
(set! texture (load-texture "plt-logo-red-gradient.png" #:repeat 'both)))
(define (draw)
; the coordinates
(define vertex-array
(f64vector -0.5 -0.5
0.5 -0.5
0.5 0.5
-0.5 0.5))
(define texcoord-array
(s16vector 0 2
2 2
2 0
0 0))
(glBindTexture GL_TEXTURE_2D texture)
(glEnable GL_TEXTURE_2D)
(glBlendFunc GL_ONE GL_ONE_MINUS_SRC_ALPHA) ; This is the correct setting for pre-multiplied alpha.
(glEnable GL_BLEND)
; Let's be "modern" and use the array functions (introduced in OpenGL 1.1).
; Note that you need to ask GL everything 3 times:
; 1. Here is an array I'd like you to draw...
(let-values (((type cptr) (gl-vector->type/cpointer vertex-array)))
(glVertexPointer 2 type 0 cptr))
(let-values (((type cptr) (gl-vector->type/cpointer texcoord-array)))
(glTexCoordPointer 2 type 0 cptr))
; 2. Yes, I really want you to use it, I was not simply fooling around.
(glEnableClientState GL_VERTEX_ARRAY)
(glEnableClientState GL_TEXTURE_COORD_ARRAY)
; 3. Allright, now draw the silly thing already!
(glDrawArrays GL_QUADS 0 4)
; Clean up state.
(glDisableClientState GL_TEXTURE_COORD_ARRAY)
(glDisableClientState GL_VERTEX_ARRAY))
(view draw setup)
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