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/*
* glClear + glScissor + Undefined content of framebuffer
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <GL/glut.h>
GLenum doubleBuffer;
GLint Width = 200, Height = 150;
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));
fprintf(stderr, "Top right corner should be red\n");
fflush(stderr);
}
static void Reshape(int width, int height)
{
Width = width;
Height = height;
glViewport(0, 0, (GLint)width, (GLint)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(1);
default:
glutPostRedisplay();
return;
}
}
static void Draw(void)
{
glColor4f(1.0, 0.0, 0.0, 1.0);
glBegin(GL_QUADS);
glVertex2d(0.0, 0.0);
glVertex2d(0.0, 1.0);
glVertex2d(1.0, 1.0);
glVertex2d(1.0, 0.0);
glEnd();
glBegin(GL_QUADS);
glVertex2d(0.0, 0.0);
glVertex2d(0.0, -1.0);
glVertex2d(1.0, -1.0);
glVertex2d(1.0, 0.0);
glEnd();
glEnable(GL_SCISSOR_TEST);
glClearColor(1, 1, 0, 0);
glScissor(Width / 2, 0, Width - Width / 2, Height / 2);
glClear(GL_COLOR_BUFFER_BIT);
glClearColor(0, 0, 1, 0);
glScissor(0, Height / 2, Width / 2, Height - Height / 2);
glClear(GL_COLOR_BUFFER_BIT);
glDisable(GL_SCISSOR_TEST);
glColor4f(0.0, 1.0, 0.0, 1.0);
glBegin(GL_QUADS);
glVertex2d( 0.0, 0.0);
glVertex2d( 0.0, -1.0);
glVertex2d(-1.0, -1.0);
glVertex2d(-1.0, 0.0);
glEnd();
glFlush();
if (doubleBuffer) {
glutSwapBuffers();
}
}
static GLenum Args(int argc, char **argv)
{
GLint i;
doubleBuffer = GL_TRUE;
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(0, 0); glutInitWindowSize( Width, Height );
type = GLUT_RGB | GLUT_ALPHA;
type |= (doubleBuffer) ? GLUT_DOUBLE : GLUT_SINGLE;
glutInitDisplayMode(type);
if (glutCreateWindow(argv[0]) == GL_FALSE) {
exit(1);
}
Init();
Reshape(Width, Height);
glutReshapeFunc(Reshape);
glutKeyboardFunc(Key);
glutDisplayFunc(Draw);
glutMainLoop();
return 0;
}
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