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// Built off the Triangle and Checkered Triangle OpenGL examples by Ray Toal
// (https://cs.lmu.edu/~ray/notes/openglexamples/)
#include <stdio.h>
#include <GL/glut.h>
#define red {0xff, 0x00, 0x00}
#define yellow {0xff, 0xff, 0x00}
#define magenta {0xff, 0, 0xff}
GLubyte* texture;
const unsigned side = 1024*10; // 30 MiB
// Clears the current window and draws a triangle.
void display() {
// Set every pixel in the frame buffer to the current clear color.
glClear(GL_COLOR_BUFFER_BIT);
// Re-upload the texture on every frame
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, side, side, GL_RGB, GL_UNSIGNED_BYTE, texture);
// Drawing is done by specifying a sequence of vertices. The way these
// vertices are connected (or not connected) depends on the argument to
// glBegin. GL_POLYGON constructs a filled polygon.
glBegin(GL_POLYGON);
glTexCoord2f(0.5, side); glVertex3f(-0.6, -0.75, 0.5);
glTexCoord2f(0.0, 0.0); glVertex3f(0.6, -0.75, 0);
glTexCoord2f(side, 0.0); glVertex3f(0, 0.75, 0);
glEnd();
// Flush drawing command buffer to make drawing happen as soon as possible.
glFlush();
// Request a redraw on the next loop
glutPostRedisplay();
}
// Initializes GLUT, the display mode, and main window; registers callbacks;
// enters the main event loop.
int main(int argc, char** argv) {
// No arguments are accepted
if (argc != 1) {
fprintf(stderr, "Usage: %s\n", argv[0]);
return 1;
}
// 30 MiB image
texture = malloc(side*side*3u);
// Add a checkered pattern to the texture
for (unsigned i = 0; i < side*side; i++) {
if (i % 2 == 0) { // Yellow
texture[i*3] = 0xff;
texture[i*3+1] = 0xff;
} else // Red
texture[i*3] = 0xff;
}
// Use a single buffered window in RGB mode (as opposed to a double-buffered
// window or color-index mode).
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
// Position window at (80,80)-(480,380) and give it a title.
glutInitWindowPosition(80, 80);
glutInitWindowSize(400, 300);
glutCreateWindow("A Simple Triangle");
// Tell GLUT that whenever the main window needs to be repainted that it
// should call the function display().
glutDisplayFunc(display);
glEnable(GL_TEXTURE_2D);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glTexImage2D(GL_TEXTURE_2D,
0, // level 0
3, // use only R, G, and B components
side, side, // texture has 2x2 texels
0, // no border
GL_RGB, // texels are in RGB format
GL_UNSIGNED_BYTE, // color components are unsigned bytes
texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
// Tell GLUT to start reading and processing events. This function
// never returns; the program only exits when the user closes the main
// window or kills the process.
glutMainLoop();
}
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