git.sesse.net Git - movit/blob - init.cpp

   1 #include "init.h"
   2 #include "opengl.h"
   3 #include "util.h"
   4
   5 bool movit_initialized = false;
   6 float movit_texel_subpixel_precision;
   7
   8 namespace {
   9
  10 void measure_texel_subpixel_precision()
  11 {
  12         static const unsigned width = 1024;
  13
  14         // Generate a destination texture to render to, and an FBO.
  15         GLuint dst_texnum, fbo;
  16
  17         glGenTextures(1, &dst_texnum);
  18         check_error();
  19         glBindTexture(GL_TEXTURE_2D, dst_texnum);
  20         check_error();
  21         glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA16F_ARB, width, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
  22         check_error();
  23
  24         glGenFramebuffers(1, &fbo);
  25         check_error();
  26         glBindFramebuffer(GL_FRAMEBUFFER, fbo);
  27         check_error();
  28         glFramebufferTexture2D(
  29                 GL_FRAMEBUFFER,
  30                 GL_COLOR_ATTACHMENT0,
  31                 GL_TEXTURE_2D,
  32                 dst_texnum,
  33                 0);
  34         check_error();
  35
  36         // Now generate a simple texture that's just [0,1].
  37         GLuint src_texnum;
  38         float texdata[] = { 0, 1 };
  39         glGenTextures(1, &dst_texnum);
  40         check_error();
  41         glBindTexture(GL_TEXTURE_1D, dst_texnum);
  42         check_error();
  43         glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
  44         check_error();
  45         glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
  46         check_error();
  47         glTexImage1D(GL_TEXTURE_1D, 0, GL_LUMINANCE16F_ARB, 2, 0, GL_LUMINANCE, GL_FLOAT, texdata);
  48         check_error();
  49         glEnable(GL_TEXTURE_1D);
  50         check_error();
  51
  52         // Basic state.
  53         glDisable(GL_BLEND);
  54         check_error();
  55         glDisable(GL_DEPTH_TEST);
  56         check_error();
  57         glDepthMask(GL_FALSE);
  58         check_error();
  59
  60         glViewport(0, 0, width, 1);
  61
  62         glMatrixMode(GL_PROJECTION);
  63         glLoadIdentity();
  64         glOrtho(0.0, 1.0, 0.0, 1.0, 0.0, 1.0);
  65
  66         glMatrixMode(GL_MODELVIEW);
  67         glLoadIdentity();
  68         check_error();
  69
  70         // Draw the texture stretched over a long quad, interpolating it out.
  71         // Note that since the texel center is in (0.5), we need to adjust the
  72         // texture coordinates in order not to get long stretches of (1,1,1,...)
  73         // at the start and (...,0,0,0) at the end.
  74         glBegin(GL_QUADS);
  75
  76         glTexCoord1f(0.25f);
  77         glVertex2f(0.0f, 0.0f);
  78
  79         glTexCoord1f(0.75f);
  80         glVertex2f(1.0f, 0.0f);
  81
  82         glTexCoord1f(0.75f);
  83         glVertex2f(1.0f, 1.0f);
  84
  85         glTexCoord1f(0.25f);
  86         glVertex2f(0.0f, 1.0f);
  87
  88         glEnd();
  89         check_error();
  90
  91         glDisable(GL_TEXTURE_1D);
  92         check_error();
  93
  94         // Now read the data back and see what the card did.
  95         // (We only look at the red channel; the others will surely be the same.)
  96         // We assume a linear ramp; anything else will give sort of odd results here.
  97         float out_data[width];
  98         glReadPixels(0, 0, width, 1, GL_RED, GL_FLOAT, out_data);
  99         check_error();
 100
 101         float biggest_jump = 0.0f;
 102         for (unsigned i = 1; i < width; ++i) {
 103                 assert(out_data[i] >= out_data[i - 1]);
 104                 biggest_jump = std::max(biggest_jump, out_data[i] - out_data[i - 1]);
 105         }
 106
 107         movit_texel_subpixel_precision = biggest_jump;
 108
 109         // Clean up.
 110         glBindTexture(GL_TEXTURE_1D, 0);
 111         check_error();
 112         glBindFramebuffer(GL_FRAMEBUFFER, 0);
 113         check_error();
 114         glDeleteFramebuffers(1, &fbo);
 115         check_error();
 116         glDeleteTextures(1, &dst_texnum);
 117         check_error();
 118         glDeleteTextures(1, &src_texnum);
 119         check_error();
 120 }
 121
 122 }  // namespace
 123
 124 void init_movit()
 125 {
 126         if (movit_initialized) {
 127                 return;
 128         }
 129
 130         // geez
 131         glPixelStorei(GL_PACK_ALIGNMENT, 1);
 132         glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
 133
 134         measure_texel_subpixel_precision();
 135
 136         movit_initialized = true;
 137 }