1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
|
/*
* glRead/DrawPixels test
*/
#define GL_GLEXT_PROTOTYPES
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <GL/glut.h>
static int Width = 250, Height = 250;
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));
glClearColor(0.3, 0.1, 0.3, 0.0);
}
static void Reshape(int width, int height)
{
Width = width / 2;
Height = height;
/* draw on left half (we'll read that area) */
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);
}
static void Key(unsigned char key, int x, int y)
{
switch (key) {
case 27:
exit(0);
default:
return;
}
glutPostRedisplay();
}
static void Draw(void)
{
GLfloat *image = (GLfloat *) malloc(Width * Height * 4 * sizeof(GLfloat));
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_TRIANGLES);
glColor3f(.8,0,0);
glVertex3f(-0.9, -0.9, -30.0);
glColor3f(0,.9,0);
glVertex3f( 0.9, -0.9, -30.0);
glColor3f(0,0,.7);
glVertex3f( 0.0, 0.9, -30.0);
glEnd();
glReadPixels(0, 0, Width, Height, GL_RGBA, GL_FLOAT, image);
printf("Pixel(0,0) = %f, %f, %f, %f\n",
image[0], image[1], image[2], image[3]);
/* draw to right half of window */
glWindowPos2iARB(Width, 0);
glDrawPixels(Width, Height, GL_RGBA, GL_FLOAT, image);
free(image);
glutSwapBuffers();
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitWindowPosition(0, 0);
glutInitWindowSize(Width*2, Height);
glutInitDisplayMode(GLUT_RGB | GLUT_ALPHA | GLUT_DOUBLE);
if (glutCreateWindow(argv[0]) == GL_FALSE) {
exit(1);
}
Init();
glutReshapeFunc(Reshape);
glutKeyboardFunc(Key);
glutDisplayFunc(Draw);
glutMainLoop();
return 0;
}
|
