1 /*
2 * glClear + glScissor + Undefined content of framebuffer
3 */
4
5 #include <stdio.h>
6 #include <string.h>
7 #include <stdlib.h>
8 #include "glut_wrap.h"
9
10
11 GLenum doubleBuffer;
12 GLint Width = 200, Height = 150;
13
Init(void)14 static void Init(void)
15 {
16 fprintf(stderr, "GL_RENDERER = %s\n", (char *) glGetString(GL_RENDERER));
17 fprintf(stderr, "GL_VERSION = %s\n", (char *) glGetString(GL_VERSION));
18 fprintf(stderr, "GL_VENDOR = %s\n", (char *) glGetString(GL_VENDOR));
19 fprintf(stderr, "Top right corner should be red\n");
20 fflush(stderr);
21 }
22
Reshape(int width,int height)23 static void Reshape(int width, int height)
24 {
25 Width = width;
26 Height = height;
27
28 glViewport(0, 0, (GLint)width, (GLint)height);
29
30 glMatrixMode(GL_PROJECTION);
31 glLoadIdentity();
32 glOrtho(-1.0, 1.0, -1.0, 1.0, -0.5, 1000.0);
33 glMatrixMode(GL_MODELVIEW);
34 }
35
Key(unsigned char key,int x,int y)36 static void Key(unsigned char key, int x, int y)
37 {
38 switch (key) {
39 case 27:
40 exit(1);
41 default:
42 glutPostRedisplay();
43 return;
44 }
45
46 }
47
Draw(void)48 static void Draw(void)
49 {
50 glColor4f(1.0, 0.0, 0.0, 1.0);
51 glBegin(GL_QUADS);
52 glVertex2d(0.0, 0.0);
53 glVertex2d(0.0, 1.0);
54 glVertex2d(1.0, 1.0);
55 glVertex2d(1.0, 0.0);
56 glEnd();
57
58 glBegin(GL_QUADS);
59 glVertex2d(0.0, 0.0);
60 glVertex2d(0.0, -1.0);
61 glVertex2d(1.0, -1.0);
62 glVertex2d(1.0, 0.0);
63 glEnd();
64
65 glEnable(GL_SCISSOR_TEST);
66 glClearColor(1, 1, 0, 0);
67 glScissor(Width / 2, 0, Width - Width / 2, Height / 2);
68 glClear(GL_COLOR_BUFFER_BIT);
69
70 glClearColor(0, 0, 1, 0);
71 glScissor(0, Height / 2, Width / 2, Height - Height / 2);
72 glClear(GL_COLOR_BUFFER_BIT);
73 glDisable(GL_SCISSOR_TEST);
74
75 glColor4f(0.0, 1.0, 0.0, 1.0);
76 glBegin(GL_QUADS);
77 glVertex2d( 0.0, 0.0);
78 glVertex2d( 0.0, -1.0);
79 glVertex2d(-1.0, -1.0);
80 glVertex2d(-1.0, 0.0);
81 glEnd();
82
83 glFlush();
84
85 if (doubleBuffer) {
86 glutSwapBuffers();
87 }
88 }
89
Args(int argc,char ** argv)90 static GLenum Args(int argc, char **argv)
91 {
92 GLint i;
93
94 doubleBuffer = GL_TRUE;
95
96 for (i = 1; i < argc; i++) {
97 if (strcmp(argv[i], "-sb") == 0) {
98 doubleBuffer = GL_FALSE;
99 } else if (strcmp(argv[i], "-db") == 0) {
100 doubleBuffer = GL_TRUE;
101 } else {
102 fprintf(stderr, "%s (Bad option).\n", argv[i]);
103 return GL_FALSE;
104 }
105 }
106 return GL_TRUE;
107 }
108
main(int argc,char ** argv)109 int main(int argc, char **argv)
110 {
111 GLenum type;
112
113 glutInit(&argc, argv);
114
115 if (Args(argc, argv) == GL_FALSE) {
116 exit(1);
117 }
118
119 glutInitWindowPosition(0, 0); glutInitWindowSize( Width, Height );
120
121
122 type = GLUT_RGB | GLUT_ALPHA;
123 type |= (doubleBuffer) ? GLUT_DOUBLE : GLUT_SINGLE;
124 glutInitDisplayMode(type);
125
126 if (glutCreateWindow(argv[0]) == GL_FALSE) {
127 exit(1);
128 }
129
130 Init();
131 Reshape(Width, Height);
132
133 glutReshapeFunc(Reshape);
134 glutKeyboardFunc(Key);
135 glutDisplayFunc(Draw);
136 glutMainLoop();
137 return 0;
138 }
139