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110 lines
2.8 KiB
C
110 lines
2.8 KiB
C
/*
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# glNormal
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http://stackoverflow.com/questions/5906993/what-is-a-normal-in-opengl/36087311#36087311
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http://gamedev.stackexchange.com/questions/50653/opengl-why-do-i-have-to-set-a-normal-with-glnormal/118476#118476
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*/
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#include <stdlib.h>
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#include <GL/gl.h>
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#include <GL/glu.h>
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#include <GL/glut.h>
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/* Triangle on the x-y plane. */
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static void draw_triangle() {
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glBegin(GL_TRIANGLES);
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glVertex3f( 0.0f, 1.0f, 0.0f);
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glVertex3f(-1.0f, -1.0f, 0.0f);
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glVertex3f( 1.0f, -1.0f, 0.0f);
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glEnd();
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}
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/* A triangle tilted 45 degrees manually. */
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static void draw_triangle_45() {
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glBegin(GL_TRIANGLES);
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glVertex3f( 0.0f, 1.0f, -1.0f);
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glVertex3f(-1.0f, -1.0f, 0.0f);
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glVertex3f( 1.0f, -1.0f, 0.0f);
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glEnd();
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}
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static void display(void) {
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glColor3f(1.0f, 0.0f, 0.0f);
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glClear(GL_COLOR_BUFFER_BIT);
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glPushMatrix();
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/*
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Triangle perpendicular to the light.
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0,0,1 also happens to be the default normal if we hadn't specified one.
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*/
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glNormal3f(0.0f, 0.0f, 1.0f);
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draw_triangle();
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/*
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This triangle is as bright as the previous one.
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This is not photorealistic, where it should be less bright.
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*/
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glTranslatef(2.0f, 0.0f, 0.0f);
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draw_triangle_45();
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/*
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Same as previous triangle, but with the normal set
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to the photorealistic value of 45, making it less bright.
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*/
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glTranslatef(2.0f, 0.0f, 0.0f);
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glNormal3f(0.0f, 1.0f, 1.0f);
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draw_triangle_45();
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/*
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This triangle is rotated 45 degrees with a glRotate.
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It should be as bright as the previous one,
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even though we set the normal to 0,0,1.
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So glRotate also affects the normal!
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*/
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glTranslatef(2.0f, 0.0f, 0.0f);
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glNormal3f(0.0, 0.0, 1.0);
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glRotatef(45.0, -1.0, 0.0, 0.0);
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draw_triangle();
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glPopMatrix();
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glFlush();
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}
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static void init(void) {
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GLfloat light0_diffuse[] = {1.0, 1.0, 1.0, 1.0};
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/* Plane wave coming from +z infinity. */
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GLfloat light0_position[] = {0.0, 0.0, 1.0, 0.0};
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glClearColor(0.0, 0.0, 0.0, 0.0);
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glShadeModel(GL_SMOOTH);
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glLightfv(GL_LIGHT0, GL_POSITION, light0_position);
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glLightfv(GL_LIGHT0, GL_DIFFUSE, light0_diffuse);
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glEnable(GL_LIGHTING);
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glEnable(GL_LIGHT0);
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glColorMaterial(GL_FRONT, GL_DIFFUSE);
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glEnable(GL_COLOR_MATERIAL);
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glEnable(GL_NORMALIZE);
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}
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static void reshape(int w, int h) {
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glViewport(0, 0, w, h);
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glMatrixMode(GL_PROJECTION);
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glLoadIdentity();
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glOrtho(-1.0, 7.0, -1.0, 1.0, -1.5, 1.5);
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glMatrixMode(GL_MODELVIEW);
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glLoadIdentity();
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}
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int main(int argc, char** argv) {
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glutInit(&argc, argv);
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glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
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glutInitWindowSize(800, 200);
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glutInitWindowPosition(100, 100);
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glutCreateWindow(argv[0]);
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init();
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glutDisplayFunc(display);
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glutReshapeFunc(reshape);
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glutMainLoop();
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return EXIT_SUCCESS;
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}
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