src/glsl/points.c

   1 /**
   2  * Implement smooth (AA) points with shaders.
   3  * A simple variation could be used for sprite points.
   4  * Brian Paul
   5  * 29 July 2007
   6  */
   7
   8 #include <assert.h>
   9 #include <string.h>
  10 #include <stdio.h>
  11 #include <stdlib.h>
  12 #include <math.h>
  13 #include <GL/glew.h>
  14 #include "glut_wrap.h"
  15 #include "shaderutil.h"
  16
  17
  18 static GLuint FragShader;
  19 static GLuint VertShader;
  20 static GLuint Program;
  21
  22 static GLint Win = 0;
  23 static GLint WinWidth = 500, WinHeight = 200;
  24 static GLfloat Xpos = 0.0f, Ypos = 0.0f;
  25 static GLint uViewportInv;
  26 static GLboolean Smooth = GL_TRUE, Blend = GL_TRUE;
  27
  28
  29 /**
  30  * Issue vertices for a "shader point".
  31  * The position is duplicated, only texcoords (or other vertex attrib) change.
  32  * The vertex program will compute the "real" quad corners.
  33  */
  34 static void
  35 PointVertex3f(GLfloat x, GLfloat y, GLfloat z)
  36 {
  37    glTexCoord2f(-1, -1);
  38    glVertex3f(x, y, z);
  39
  40    glTexCoord2f( 1, -1);
  41    glVertex3f(x, y, z);
  42
  43    glTexCoord2f( 1,  1);
  44    glVertex3f(x, y, z);
  45
  46    glTexCoord2f(-1,  1);
  47    glVertex3f(x, y, z);
  48 }
  49
  50
  51 static void
  52 DrawPoints(GLboolean shaderPoints)
  53 {
  54    int i;
  55    for (i = 0; i < 9; i++) {
  56       GLfloat x = i - 4, y = 0, z = 0;
  57       /* note: can't call glPointSize inside Begin/End :( */
  58       glPointSize( 2 + i * 5 );
  59       if (shaderPoints) {
  60          glBegin(GL_QUADS);
  61          PointVertex3f(x, y, z);
  62          glEnd();
  63       }
  64       else {
  65          glBegin(GL_POINTS);
  66          glVertex3f(x, y, z);
  67          glEnd();
  68       }
  69    }
  70 }
  71
  72
  73 /**
  74  * Top row of points is rendered conventionally with GL_POINT_SMOOTH.
  75  * Bottom row is rendered with special vertex/fragment shaders (see Init()).
  76  */
  77 static void
  78 Redisplay(void)
  79 {
  80    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  81
  82    if (Smooth)
  83       glEnable(GL_POINT_SMOOTH);
  84    else
  85       glDisable(GL_POINT_SMOOTH);
  86
  87    if (Blend)
  88       glEnable(GL_BLEND);
  89    else
  90       glDisable(GL_BLEND);
  91
  92    glPushMatrix();
  93    glTranslatef(Xpos, Ypos, 0);
  94
  95    /*
  96     * regular points
  97     */
  98    glPushMatrix();
  99    glTranslatef(0, 1.2, 0);
 100    glUseProgram(0);
 101    DrawPoints(GL_FALSE);
 102    glPopMatrix();
 103
 104    /*
 105     * shader points
 106     */
 107    glPushMatrix();
 108    glTranslatef(0, -1.2, 0);
 109    glUseProgram(Program);
 110    if (uViewportInv != -1) {
 111       glUniform2f(uViewportInv, 1.0 / WinWidth, 1.0 / WinHeight);
 112    }
 113    DrawPoints(GL_TRUE);
 114    glPopMatrix();
 115
 116    glPopMatrix();
 117
 118    glutSwapBuffers();
 119 }
 120
 121
 122 static void
 123 Reshape(int width, int height)
 124 {
 125    WinWidth = width;
 126    WinHeight = height;
 127    glViewport(0, 0, width, height);
 128    glMatrixMode(GL_PROJECTION);
 129    glLoadIdentity();
 130    glFrustum(-1.0, 1.0, -1.0, 1.0, 4.0, 30.0);
 131    glMatrixMode(GL_MODELVIEW);
 132    glLoadIdentity();
 133    glTranslatef(0.0f, 0.0f, -20.0f);
 134 }
 135
 136
 137 static void
 138 Key(unsigned char key, int x, int y)
 139 {
 140   (void) x;
 141   (void) y;
 142
 143    switch(key) {
 144    case 'b':
 145       Blend = !Blend;
 146       break;
 147    case 's':
 148       Smooth = !Smooth;
 149       break;
 150    case 27:
 151       glDeleteShader(FragShader);
 152       glDeleteShader(VertShader);
 153       glDeleteProgram(Program);
 154       glutDestroyWindow(Win);
 155       exit(0);
 156    }
 157    glutPostRedisplay();
 158 }
 159
 160
 161 static void
 162 SpecialKey(int key, int x, int y)
 163 {
 164    const GLfloat step = 1/100.0;
 165    switch(key) {
 166    case GLUT_KEY_UP:
 167       Ypos += step;
 168       break;
 169    case GLUT_KEY_DOWN:
 170       Ypos -= step;
 171       break;
 172    case GLUT_KEY_LEFT:
 173       Xpos -= step;
 174       break;
 175    case GLUT_KEY_RIGHT:
 176       Xpos += step;
 177       break;
 178    }
 179    glutPostRedisplay();
 180 }
 181
 182
 183 static void
 184 Init(void)
 185 {
 186    /* Fragment shader: compute distance of fragment from center of point
 187     * (we're using texcoords but another varying could be used).
 188     *   if dist > 1, discard (coverage==0)
 189     *   if dist < k, coverage = 1
 190     *   else, coverage = func(dist)
 191     * Note: length() uses sqrt() and may be expensive.  The distance could
 192     * be squared instead (with adjustments to the threshold (k) test)
 193     */
 194    static const char *fragShaderText =
 195       "void main() {\n"
 196       "   float cover; \n"
 197       "   float k = 2.0 / gl_Point.size; \n"
 198       "   float d = length(gl_TexCoord[0].xy); \n"
 199       "   if (d >= 1.0) \n"
 200       "      discard; \n"
 201       "   if (d < 1.0 - k) \n"
 202       "      cover = 1.0; \n"
 203       "   else \n"
 204       "      cover = (1.0 - d) * 0.5 * gl_Point.size; \n"
 205       "   gl_FragColor.rgb = gl_Color.rgb; \n"
 206       "   gl_FragColor.a = cover; \n"
 207       "}\n";
 208    /* Vertex shader: compute new vertex position based on incoming vertex pos,
 209     * texcoords, point size, and inverse viewport scale factor.
 210     * Note: should compute point size attenuation here too.
 211     */
 212    static const char *vertShaderText =
 213       "uniform vec2 viewportInv; \n"
 214       "void main() {\n"
 215       "   vec4 pos = gl_ModelViewProjectionMatrix * gl_Vertex;\n"
 216       "   gl_Position.xy = pos.xy + gl_MultiTexCoord0.xy * viewportInv \n"
 217       "                    * gl_Point.size * pos.w; \n"
 218       "   gl_Position.zw = pos.zw; \n"
 219       "   gl_TexCoord[0] = gl_MultiTexCoord0; \n"
 220       "   gl_FrontColor = gl_Color; \n"
 221       "}\n";
 222
 223    if (!ShadersSupported())
 224       exit(1);
 225
 226    VertShader = CompileShaderText(GL_VERTEX_SHADER, vertShaderText);
 227    FragShader = CompileShaderText(GL_FRAGMENT_SHADER, fragShaderText);
 228    Program = LinkShaders(VertShader, FragShader);
 229
 230    glUseProgram(Program);
 231
 232    uViewportInv = glGetUniformLocation(Program, "viewportInv");
 233
 234    glUseProgram(0);
 235
 236    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 237 }
 238
 239
 240 int
 241 main(int argc, char *argv[])
 242 {
 243    glutInit(&argc, argv);
 244    glutInitWindowSize(WinWidth, WinHeight);
 245    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
 246    Win = glutCreateWindow(argv[0]);
 247    glewInit();
 248    glutReshapeFunc(Reshape);
 249    glutKeyboardFunc(Key);
 250    glutSpecialFunc(SpecialKey);
 251    glutDisplayFunc(Redisplay);
 252    Init();
 253    glutMainLoop();
 254    return 0;
 255 }
 256
 257