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/* Copyright (c) Mark J. Kilgard, 1996. */
/* This program is freely distributable without licensing fees
and is provided without guarantee or warrantee expressed or
implied. This program is -not- in the public domain. */
/* This program is a response to a question posed by Gil Colgate
<gcolgate@sirius.com> about how lengthy a program is required using
OpenGL compared to using Direct3D immediate mode to "draw a
triangle at screen coordinates 0,0, to 200,200 to 20,200, and I
want it to be blue at the top vertex, red at the left vertex, and
green at the right vertex". I'm not sure how long the Direct3D
program is; Gil has used Direct3D and his guess is "about 3000
lines of code". */
/* X compile line: cc -o simple simple.c -lglut -lGLU -lGL -lXmu -lXext -lX11 -lm */
#include <GL/glut.h>
void
reshape(int w, int h)
{
/* Because Gil specified "screen coordinates" (presumably with an
upper-left origin), this short bit of code sets up the coordinate
system to correspond to actual window coodrinates. This code
wouldn't be required if you chose a (more typical in 3D) abstract
coordinate system. */
glViewport(0, 0, w, h); /* Establish viewing area to cover entire window. */
glMatrixMode(GL_PROJECTION); /* Start modifying the projection matrix. */
glLoadIdentity(); /* Reset project matrix. */
glOrtho(0, w, 0, h, -1, 1); /* Map abstract coords directly to window coords. */
glScalef(1, -1, 1); /* Invert Y axis so increasing Y goes down. */
glTranslatef(0, -h, 0); /* Shift origin up to upper-left corner. */
}
void
display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_TRIANGLES);
glColor3f(0.0, 0.0, 1.0); /* blue */
glVertex2i(0, 0);
glColor3f(0.0, 1.0, 0.0); /* green */
glVertex2i(200, 200);
glColor3f(1.0, 0.0, 0.0); /* red */
glVertex2i(20, 200);
glEnd();
glFlush(); /* Single buffered, so needs a flush. */
}
int
main(int argc, char **argv)
{
glutInit(&argc, argv);
glutCreateWindow("single triangle");
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutMainLoop();
return 0; /* ANSI C requires main to return int. */
}
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