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#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <glad/glad.h>
#include "glut_wrap.h"
static int Width = 512, Height = 512;
static GLuint MyFB, MyRB;
#define CheckError() assert(glGetError() == 0)
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));
fflush(stderr);
if (!glutExtensionSupported("GL_EXT_framebuffer_object")) {
printf("GL_EXT_framebuffer_object not found!\n");
exit(0);
}
glGenFramebuffersEXT(1, &MyFB);
glGenRenderbuffersEXT(1, &MyRB);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, MyFB);
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, MyRB);
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT1_EXT,
GL_RENDERBUFFER_EXT, MyRB);
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_RGB, Width, Height);
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;
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_RGB, Width, Height);
}
static void
Key(unsigned char key, int x, int y)
{
if (key == 27)
exit(0);
glutPostRedisplay();
}
static void
Draw(void)
{
/* draw to user framebuffer */
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, MyFB);
glDrawBuffer(GL_COLOR_ATTACHMENT1_EXT);
glReadBuffer(GL_COLOR_ATTACHMENT1_EXT);
glViewport(0, 0, Width, Height);
CheckError();
/* Clear the FBO to gray-blue */
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();
printf("Pixel(0,0) = %d, %d, %d, %d\n",
buffer[0], buffer[1], buffer[2], buffer[3]);
fflush(stdout);
/* 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();
}
glutSwapBuffers();
CheckError();
}
int
main(int argc, char *argv[])
{
glutInit(&argc, argv);
glutInitWindowPosition(100, 0);
glutInitWindowSize(Width, Height);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
if (glutCreateWindow(argv[0]) == GL_FALSE) {
exit(1);
}
gladLoadGL();
Init();
glutReshapeFunc(Reshape);
glutKeyboardFunc(Key);
glutDisplayFunc(Draw);
glutMainLoop();
return 0;
}
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