Add an implementation of RPDF dither on the final output.

[movit] / dither_effect.cpp

diff --git a/dither_effect.cpp b/dither_effect.cpp
new file mode 100644 (file)
index 0000000..cdfb157
--- /dev/null
+++ b/dither_effect.cpp
@@ -0,0 +1,94 @@
+#include <math.h>
+#include <assert.h>
+
+#include "dither_effect.h"
+#include "util.h"
+#include "opengl.h"
+
+namespace {
+
+// A simple LCG (linear congruental generator) random generator.
+// We implement our own so we can be deterministic from frame to frame
+// and run to run; we don't have special needs for speed or quality,
+// as long as the period is reasonably long. The output is in range
+// [0, 2^31>.
+//
+// This comes from http://en.wikipedia.org/wiki/Linear_congruential_generator.
+unsigned lcg_rand(unsigned x)
+{
+       return (x * 1103515245U + 12345U) & ((1U << 31) - 1);
+} 
+
+}  // namespace
+
+DitherEffect::DitherEffect()
+       : width(1280), height(720), num_bits(8),
+         last_width(-1), last_height(-1), last_num_bits(-1)
+{
+       register_int("output_width", &width);
+       register_int("output_height", &height);
+       register_int("num_bits", &num_bits);
+
+       glGenTextures(1, &texnum);
+}
+
+DitherEffect::~DitherEffect()
+{
+       glDeleteTextures(1, &texnum);
+}
+
+std::string DitherEffect::output_fragment_shader()
+{
+       return read_file("dither_effect.frag");
+}
+
+void DitherEffect::update_texture(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num)
+{
+       float *dither_noise = new float[width * height];
+       float dither_double_amplitude = 1.0f / (1 << num_bits);
+
+       // Using the resolution as a seed gives us a consistent dither from frame to frame.
+       // It also gives a different dither for e.g. different aspect ratios, which _feels_
+       // good, but probably shouldn't matter.
+       unsigned seed = (width << 16) ^ height;
+       for (int i = 0; i < width * height; ++i) {
+               seed = lcg_rand(seed);
+               float normalized_rand = seed * (1.0f / (1U << 31)) - 0.5;  // [-0.5, 0.5>
+               dither_noise[i] = dither_double_amplitude * normalized_rand;
+       }
+
+       glActiveTexture(GL_TEXTURE0 + *sampler_num);
+       check_error();
+       glBindTexture(GL_TEXTURE_2D, texnum);
+       check_error();
+       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+       check_error();
+       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+       check_error();
+       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+       check_error();
+       glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE16F_ARB, width, height, 0, GL_LUMINANCE, GL_FLOAT, dither_noise);
+       check_error();
+
+       delete[] dither_noise;
+}
+
+void DitherEffect::set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num)
+{
+       Effect::set_gl_state(glsl_program_num, prefix, sampler_num);
+
+       if (width != last_width || height != last_height || num_bits != last_num_bits) {
+               update_texture(glsl_program_num, prefix, sampler_num);
+               last_width = width;
+               last_height = height;
+               last_num_bits = num_bits;
+       }
+
+       glActiveTexture(GL_TEXTURE0 + *sampler_num);
+       check_error();
+       glBindTexture(GL_TEXTURE_2D, texnum);
+       check_error();
+
+       set_uniform_int(glsl_program_num, prefix, "dither_tex", *sampler_num);
+       ++sampler_num;
+}