src/tests/shader-interp.c

   1 /**
   2  * Test conversion of a perspective-interpolated value to be a linearly
   3  * interpolated value.
   4  * Brian Paul
   5  * 22 March 2011
   6  */
   7
   8
   9 #include <assert.h>
  10 #include <string.h>
  11 #include <stdio.h>
  12 #include <stdlib.h>
  13 #include <math.h>
  14 #include <GL/glew.h>
  15 #include "glut_wrap.h"
  16 #include "shaderutil.h"
  17
  18
  19 static GLuint VertShader1, VertShader2;
  20 static GLuint FragShader1, FragShader2;
  21 static GLuint Program1, Program2;
  22 static GLint Win = 0;
  23 static int Width = 600, Height = 300;
  24
  25
  26 static void
  27 Redisplay(void)
  28 {
  29    GLuint i;
  30
  31    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  32
  33    /* draw left and right perspective projected quads */
  34    for (i = 0; i < 2; i++) {
  35       glPushMatrix();
  36
  37          if (i == 0) {
  38             glUseProgram(Program1);
  39             glViewport(0, 0, 300, 300);
  40          }
  41          else {
  42             glUseProgram(Program2);
  43             glViewport(300, 0, 300, 300);
  44          }
  45
  46          glScalef(0.9, 0.9, 1.0);
  47
  48          glBegin(GL_POLYGON);
  49          glTexCoord2f(0, 0);   glVertex3f(-1, -1, 0);
  50          glTexCoord2f(1, 0);   glVertex3f( 1, -1, 0);
  51          glTexCoord2f(1, 1);   glVertex3f( 1,  1, -12);
  52          glTexCoord2f(0, 1);   glVertex3f(-1,  1, -12);
  53          glEnd();
  54
  55       glPopMatrix();
  56    }
  57
  58    /* draw grayscale quad in middle */
  59    glUseProgram(0);
  60    glViewport(0, 0, Width, Height);
  61    glPushMatrix();
  62       glTranslatef(0.0, -0.38, 0);
  63       glScalef(0.05, 0.52, 1.0);
  64       glBegin(GL_POLYGON);
  65       glColor3f(0, 0, 0);   glVertex2f(-1, -1);
  66       glColor3f(0, 0, 0);   glVertex2f( 1, -1);
  67       glColor3f(1, 1, 1);   glVertex2f( 1,  1);
  68       glColor3f(1, 1, 1);   glVertex2f(-1,  1);
  69       glEnd();
  70    glPopMatrix();
  71
  72    if (0) {
  73       GLfloat buf1[300*4], buf2[300*4];
  74       GLuint i;
  75       glReadPixels(Width * 1 / 4, 0, 1, Height, GL_RGBA, GL_FLOAT, buf1);
  76       glReadPixels(Width * 3 / 4, 0, 1, Height, GL_RGBA, GL_FLOAT, buf2);
  77       for (i = 1; i < Height; i++) {
  78          printf("row %d:  %f (delta %f)  %f (delta %f)\n",
  79                 i,
  80                 buf1[i*4], buf1[i*4] - buf1[i*4-4],
  81                 buf2[i*4], buf2[i*4] - buf2[i*4-4]);
  82       }
  83    }
  84
  85    glutSwapBuffers();
  86 }
  87
  88
  89 static void
  90 Reshape(int width, int height)
  91 {
  92    glViewport(0, 0, width, height);
  93    glMatrixMode(GL_PROJECTION);
  94    glLoadIdentity();
  95    glFrustum(-1, 1, -1, 1, 2, 200);
  96    glMatrixMode(GL_MODELVIEW);
  97    glLoadIdentity();
  98    glTranslatef(0, 0, -2);
  99
 100    Width = width;
 101    Height = height;
 102 }
 103
 104
 105 static void
 106 CleanUp(void)
 107 {
 108    glDeleteShader(FragShader1);
 109    glDeleteShader(FragShader2);
 110    glDeleteShader(VertShader1);
 111    glDeleteShader(VertShader2);
 112    glDeleteProgram(Program1);
 113    glDeleteProgram(Program2);
 114    glutDestroyWindow(Win);
 115 }
 116
 117
 118 static void
 119 Key(unsigned char key, int x, int y)
 120 {
 121   (void) x;
 122   (void) y;
 123
 124    switch(key) {
 125    case 27:
 126       CleanUp();
 127       exit(0);
 128       break;
 129    }
 130    glutPostRedisplay();
 131 }
 132
 133
 134 static void
 135 Init(void)
 136 {
 137    /**
 138     * Regular perspective interpolation
 139     */
 140    static const char *VertShaderText1 =
 141       "void main() {\n"
 142       "   vec4 pos = ftransform();\n"
 143       "   gl_TexCoord[0] = gl_MultiTexCoord0; \n"
 144       "   gl_Position = pos;\n"
 145       "}\n";
 146
 147    static const char *FragShaderText1 =
 148       "void main() {\n"
 149       "   float gray = gl_TexCoord[0].y; \n"
 150       "   gl_FragColor = vec4(gray); \n"
 151       "}\n";
 152
 153    /**
 154     * Perspective interpolation, converted to linear interpolation
 155     * (put window position W in texcoord.w)
 156     */
 157    static const char *VertShaderText2 =
 158       "void main() {\n"
 159       "   vec4 pos = ftransform();\n"
 160       "   gl_TexCoord[0] = gl_MultiTexCoord0 * pos.w; \n"
 161       "   gl_TexCoord[0].w = pos.w; \n"
 162       "   gl_Position = pos;\n"
 163       "}\n";
 164
 165    static const char *FragShaderText2 =
 166       "void main() {\n"
 167       "   float gray = gl_TexCoord[0].y / gl_TexCoord[0].w; \n"
 168       "   gl_FragColor = vec4(gray); \n"
 169       "}\n";
 170
 171    if (!ShadersSupported())
 172       exit(1);
 173
 174    VertShader1 = CompileShaderText(GL_VERTEX_SHADER, VertShaderText1);
 175    VertShader2 = CompileShaderText(GL_VERTEX_SHADER, VertShaderText2);
 176
 177    FragShader1 = CompileShaderText(GL_FRAGMENT_SHADER, FragShaderText1);
 178    FragShader2 = CompileShaderText(GL_FRAGMENT_SHADER, FragShaderText2);
 179
 180    Program1 = LinkShaders(VertShader1, FragShader1);
 181    Program2 = LinkShaders(VertShader2, FragShader2);
 182
 183    glClearColor(0.5f, 0.5f, 0.5f, 0.0f);
 184    glEnable(GL_DEPTH_TEST);
 185
 186    printf("GL_RENDERER = %s\n",(const char *) glGetString(GL_RENDERER));
 187
 188    assert(glIsProgram(Program1));
 189    assert(glIsProgram(Program2));
 190    assert(glIsShader(VertShader1));
 191    assert(glIsShader(VertShader2));
 192    assert(glIsShader(FragShader1));
 193    assert(glIsShader(FragShader2));
 194
 195    glColor3f(1, 0, 0);
 196 }
 197
 198
 199 int
 200 main(int argc, char *argv[])
 201 {
 202    glutInit(&argc, argv);
 203    glutInitWindowSize(Width, Height);
 204    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
 205    Win = glutCreateWindow(argv[0]);
 206    glewInit();
 207    glutReshapeFunc(Reshape);
 208    glutKeyboardFunc(Key);
 209    glutDisplayFunc(Redisplay);
 210    Init();
 211    glutMainLoop();
 212    return 0;
 213 }