ALPHA.C

/* 
 * (c) Copyright 1993, Silicon Graphics, Inc. 
 *               1993-1995 Microsoft Corporation 
 * 
 * ALL RIGHTS RESERVED 
 * 
 * Please refer to OpenGL/readme.txt for additional information 
 * 
 */ 
 
/* 
 *  alpha.c 
 *  This program draws several overlapping filled polygons 
 *  to demonstrate the effect order has on alpha blending results. 
 */ 
#include "glos.h" 
 
#include <GL/gl.h> 
#include <GL/glu.h> 
#include <GL/glaux.h> 
 
void myinit(void); 
void CALLBACK myReshape(GLsizei w, GLsizei h); 
void CALLBACK display(void); 
 
/*  Initialize alpha blending function. 
 */ 
void myinit(void) 
{ 
    glEnable (GL_BLEND); 
    glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); 
    glShadeModel (GL_FLAT); 
    glClearColor (0.0, 0.0, 0.0, 0.0); 
} 
 
void CALLBACK display(void) 
{ 
    glClear(GL_COLOR_BUFFER_BIT); 
 
    glColor4f (1.0, 1.0, 0.0, 0.75); 
    glRectf (0.0, 0.0, 0.5, 1.0); 
 
    glColor4f (0.0, 1.0, 1.0, 0.75); 
    glRectf (0.0, 0.0, 1.0, 0.5); 
/*  draw colored polygons in reverse order in upper right  */ 
    glColor4f (0.0, 1.0, 1.0, 0.75); 
    glRectf (0.5, 0.5, 1.0, 1.0); 
 
    glColor4f (1.0, 1.0, 0.0, 0.75); 
    glRectf (0.5, 0.5, 1.0, 1.0); 
 
    glFlush(); 
} 
 
void CALLBACK myReshape(GLsizei w, GLsizei h) 
{ 
    if(!h) return; 
    glViewport(0, 0, w, h); 
    glMatrixMode(GL_PROJECTION); 
    glLoadIdentity(); 
    if (w <= h)  
    gluOrtho2D (0.0, 1.0, 0.0, 1.0*(GLfloat)h/(GLfloat)w); 
    else  
    gluOrtho2D (0.0, 1.0*(GLfloat)w/(GLfloat)h, 0.0, 1.0); 
    glMatrixMode(GL_MODELVIEW); 
} 
 
/*  Main Loop 
 *  Open window with initial window size, title bar,  
 *  RGBA display mode, and handle input events. 
 */ 
int main(int argc, char** argv) 
{ 
    auxInitDisplayMode (AUX_SINGLE | AUX_RGB); 
    auxInitPosition (0, 0, 500, 500); 
    auxInitWindow ("Alpha Blending"); 
    myinit(); 
    auxReshapeFunc (myReshape); 
    auxMainLoop(display); 
    return(0); 
}