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#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#define GL_GLEXT_PROTOTYPES
#include <GL/glut.h>
static GLenum TexTarget = GL_TEXTURE_2D;
static int TexWidth = 512, TexHeight = 512;
static GLenum TexIntFormat = GL_RGBA; /* either GL_RGB or GL_RGBA */
static int Width = 512, Height = 512;
static GLuint MyFB, TexObj;
#define CheckError() assert(glGetError() == 0)
GLenum doubleBuffer;
static void Init(void)
{
fprintf(stderr, "GL_RENDERER = %s\n", (char *) glGetString(GL_RENDERER));
fprintf(stderr, "GL_VERSION = %s\n", (char *) glGetString(GL_VERSION));
fprintf(stderr, "GL_VENDOR = %s\n", (char *) glGetString(GL_VENDOR));
if (!glutExtensionSupported("GL_EXT_framebuffer_object")) {
printf("GL_EXT_framebuffer_object not found!\n");
exit(0);
}
glGenFramebuffersEXT(1, &MyFB);
glGenTextures(1, &TexObj);
/* Make texture object/image */
glBindTexture(TexTarget, TexObj);
glTexParameteri(TexTarget, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(TexTarget, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(TexTarget, GL_TEXTURE_BASE_LEVEL, 0);
glTexParameteri(TexTarget, GL_TEXTURE_MAX_LEVEL, 0);
glTexImage2D(TexTarget, 0, TexIntFormat, TexWidth, TexHeight, 0,
GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
{
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, MyFB);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT,
TexTarget, TexObj, 0);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
}
}
static void
Reshape( int width, int height )
{
glViewport( 0, 0, width, height );
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
glOrtho(-1.0, 1.0, -1.0, 1.0, -0.5, 1000.0);
glMatrixMode( GL_MODELVIEW );
Width = width;
Height = height;
}
static void Key(unsigned char key, int x, int y)
{
switch (key) {
case 27:
exit(1);
default:
return;
}
glutPostRedisplay();
}
static void Draw( void )
{
/* draw to texture image */
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, MyFB);
// glDrawBuffer(GL_COLOR_ATTACHMENT1_EXT);
// glReadBuffer(GL_COLOR_ATTACHMENT1_EXT);
glViewport(0, 0, TexWidth, TexHeight);
CheckError();
glClearColor(0.5, 0.5, 1.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT);
CheckError();
if (0) {
glBegin(GL_TRIANGLES);
glColor3f(0,0,.7);
glVertex3f( 0.9, -0.9, -30.0);
glColor3f(.8,0,0);
glVertex3f( 0.9, 0.9, -30.0);
glColor3f(0,.9,0);
glVertex3f(-0.9, 0.0, -30.0);
glEnd();
}
{
GLubyte *buffer = malloc(Width * Height * 4);
/* read from user framebuffer */
glReadPixels(0, 0, Width-60, Height-60, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
CheckError();
/* draw to window */
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
glViewport(0, 0, Width, Height);
/* Try to clear the window, but will overwrite:
*/
glClearColor(0.8, 0.8, 0, 0.0);
glClear(GL_COLOR_BUFFER_BIT);
glWindowPos2iARB(30, 30);
glDrawPixels(Width-60, Height-60, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
free(buffer);
}
/* Bind normal framebuffer */
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
glViewport(0, 0, Width, Height);
if (0) {
glBegin(GL_TRIANGLES);
glColor3f(0,.7,0);
glVertex3f( 0.5, -0.5, -30.0);
glColor3f(0,0,.8);
glVertex3f( 0.5, 0.5, -30.0);
glColor3f(.9,0,0);
glVertex3f(-0.5, 0.0, -30.0);
glEnd();
}
if (doubleBuffer) {
glutSwapBuffers();
}
CheckError();
}
static GLenum Args(int argc, char **argv)
{
GLint i;
doubleBuffer = GL_FALSE;
for (i = 1; i < argc; i++) {
if (strcmp(argv[i], "-sb") == 0) {
doubleBuffer = GL_FALSE;
} else if (strcmp(argv[i], "-db") == 0) {
doubleBuffer = GL_TRUE;
} else {
fprintf(stderr, "%s (Bad option).\n", argv[i]);
return GL_FALSE;
}
}
return GL_TRUE;
}
int
main( int argc, char *argv[] )
{
GLenum type;
glutInit(&argc, argv);
if (Args(argc, argv) == GL_FALSE) {
exit(1);
}
glutInitWindowPosition(100, 0); glutInitWindowSize( Width, Height );
type = GLUT_RGB;
type |= (doubleBuffer) ? GLUT_DOUBLE : GLUT_SINGLE;
glutInitDisplayMode(type);
if (glutCreateWindow(argv[0]) == GL_FALSE) {
exit(1);
}
Init();
glutReshapeFunc(Reshape);
glutKeyboardFunc(Key);
glutDisplayFunc(Draw);
glutMainLoop();
return 0;
}
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