progs/samples/blendxor.c

   1 /*
   2 ** blendxor.c - Demonstrates the use of the blend_logic_op
   3 **    extension to draw hilights.  Using XOR to draw the same
   4 **    image twice restores the background to its original value.
   5 */
   6
   7 #include <stdio.h>
   8 #include <string.h>
   9 #ifndef _WIN32
  10 #include <unistd.h>
  11 #endif
  12 #include <stdlib.h>
  13 #include <GL/glut.h>
  14
  15
  16 GLenum doubleBuffer;
  17 int dithering = 0;
  18 GLint windW, windH;
  19
  20 static void Init(void)
  21 {
  22     glDisable(GL_DITHER);
  23     glShadeModel(GL_FLAT);
  24 }
  25
  26 static void Reshape(int width, int height)
  27 {
  28
  29     windW = (GLint)width;
  30     windH = (GLint)height;
  31
  32     glViewport(0, 0, (GLint)width, (GLint)height);
  33
  34     glMatrixMode(GL_PROJECTION);
  35     glLoadIdentity();
  36     gluOrtho2D(0, 400, 0, 400);
  37     glMatrixMode(GL_MODELVIEW);
  38 }
  39
  40 static void Key(unsigned char key, int x, int y)
  41 {
  42
  43     switch (key) {
  44       case 27:
  45         exit(1);
  46       case 'd':
  47         dithering = !dithering;
  48         break;
  49       default:
  50         return;
  51     }
  52
  53     glutPostRedisplay();
  54 }
  55
  56 static void Draw(void)
  57 {
  58     int i;
  59
  60     glDisable(GL_BLEND);
  61
  62     (dithering) ? glEnable(GL_DITHER) : glDisable(GL_DITHER);
  63
  64     glClearColor(0.5, 0.6, 0.1, 1.0);
  65     glClear(GL_COLOR_BUFFER_BIT);
  66
  67     /* Draw background prims */
  68     glColor3f(0.1, 0.1, 1.0);
  69     glBegin(GL_TRIANGLES);
  70         glVertex2i(5, 5);
  71         glVertex2i(130, 50);
  72         glVertex2i(100,  300);
  73     glEnd();
  74     glColor3f(0.5, 0.2, 0.9);
  75     glBegin(GL_TRIANGLES);
  76         glVertex2i(200, 100);
  77         glVertex2i(330, 50);
  78         glVertex2i(340,  400);
  79     glEnd();
  80
  81     glEnable(GL_BLEND);
  82     glBlendEquationEXT(GL_LOGIC_OP);
  83     glLogicOp(GL_XOR);
  84
  85     /* Draw a set of rectangles across the window */
  86     glColor3f(0.9, 0.2, 0.8);
  87     for(i = 0; i < 400; i+=60) {
  88         glBegin(GL_POLYGON);
  89             glVertex2i(i, 100);
  90             glVertex2i(i+50, 100);
  91             glVertex2i(i+50, 200);
  92             glVertex2i(i, 200);
  93         glEnd();
  94     }
  95     glFlush();   /* Added by Brian Paul */
  96 #ifndef _WIN32
  97     sleep(2);
  98 #endif
  99
 100     /* Redraw  the rectangles, which should erase them */
 101     for(i = 0; i < 400; i+=60) {
 102         glBegin(GL_POLYGON);
 103             glVertex2i(i, 100);
 104             glVertex2i(i+50, 100);
 105             glVertex2i(i+50, 200);
 106             glVertex2i(i, 200);
 107         glEnd();
 108     }
 109     glFlush();
 110
 111
 112     if (doubleBuffer) {
 113         glutSwapBuffers();
 114     }
 115 }
 116
 117 static GLenum Args(int argc, char **argv)
 118 {
 119     GLint i;
 120
 121     doubleBuffer = GL_FALSE;
 122
 123     for (i = 1; i < argc; i++) {
 124         if (strcmp(argv[i], "-sb") == 0) {
 125             doubleBuffer = GL_FALSE;
 126         } else if (strcmp(argv[i], "-db") == 0) {
 127             doubleBuffer = GL_TRUE;
 128         } else {
 129             printf("%s (Bad option).\n", argv[i]);
 130             return GL_FALSE;
 131         }
 132     }
 133     return GL_TRUE;
 134 }
 135
 136 int main(int argc, char **argv)
 137 {
 138     GLenum type;
 139     char *s;
 140     char *extName = "GL_EXT_blend_logic_op";
 141
 142     glutInit(&argc, argv);
 143
 144     if (Args(argc, argv) == GL_FALSE) {
 145         exit(1);
 146     }
 147
 148     glutInitWindowPosition(0, 0); glutInitWindowSize( 400, 400);
 149
 150     type = GLUT_RGB;
 151     type |= (doubleBuffer) ? GLUT_DOUBLE : GLUT_SINGLE;
 152     glutInitDisplayMode(type);
 153
 154     if (glutCreateWindow("Blend XOR") == GL_FALSE) {
 155         exit(1);
 156     }
 157
 158     /* Make sure blend_logic_op extension is there. */
 159     s = (char *) glGetString(GL_EXTENSIONS);
 160     if (!s)
 161         exit(1);
 162     if (strstr(s,extName) == 0) {
 163         printf("Blend_logic_op extension is not present.\n");
 164         exit(1);
 165     }
 166
 167     Init();
 168
 169     glutReshapeFunc(Reshape);
 170     glutKeyboardFunc(Key);
 171     glutDisplayFunc(Draw);
 172     glutMainLoop();
 173         return 0;
 174 }