5 #include "dither_effect.h"
6 #include "effect_util.h"
11 // A simple LCG (linear congruental generator) random generator.
12 // We implement our own so we can be deterministic from frame to frame
13 // and run to run; we don't have special needs for speed or quality,
14 // as long as the period is reasonably long. The output is in range
17 // This comes from http://en.wikipedia.org/wiki/Linear_congruential_generator.
18 unsigned lcg_rand(unsigned x)
20 return (x * 1103515245U + 12345U) & ((1U << 31) - 1);
25 DitherEffect::DitherEffect()
26 : width(1280), height(720), num_bits(8),
27 last_width(-1), last_height(-1), last_num_bits(-1)
29 register_int("output_width", &width);
30 register_int("output_height", &height);
31 register_int("num_bits", &num_bits);
33 glGenTextures(1, &texnum);
36 DitherEffect::~DitherEffect()
38 glDeleteTextures(1, &texnum);
41 std::string DitherEffect::output_fragment_shader()
43 return read_file("dither_effect.frag");
46 void DitherEffect::update_texture(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num)
48 float *dither_noise = new float[width * height];
49 float dither_double_amplitude = 1.0f / (1 << num_bits);
51 // We don't need a strictly nonrepeating dither; reducing the resolution
52 // to max 128x128 saves a lot of texture bandwidth, without causing any
53 // noticeable harm to the dither's performance.
54 texture_width = std::min(width, 128);
55 texture_height = std::min(height, 128);
57 // Using the resolution as a seed gives us a consistent dither from frame to frame.
58 // It also gives a different dither for e.g. different aspect ratios, which _feels_
59 // good, but probably shouldn't matter.
60 unsigned seed = (width << 16) ^ height;
61 for (int i = 0; i < texture_width * texture_height; ++i) {
62 seed = lcg_rand(seed);
63 float normalized_rand = seed * (1.0f / (1U << 31)) - 0.5; // [-0.5, 0.5>
64 dither_noise[i] = dither_double_amplitude * normalized_rand;
67 glActiveTexture(GL_TEXTURE0 + *sampler_num);
69 glBindTexture(GL_TEXTURE_2D, texnum);
71 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
73 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
75 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
77 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
79 glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE16F_ARB, texture_width, texture_height, 0, GL_LUMINANCE, GL_FLOAT, dither_noise);
82 delete[] dither_noise;
85 void DitherEffect::set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num)
87 Effect::set_gl_state(glsl_program_num, prefix, sampler_num);
93 if (width != last_width || height != last_height || num_bits != last_num_bits) {
94 update_texture(glsl_program_num, prefix, sampler_num);
97 last_num_bits = num_bits;
100 glActiveTexture(GL_TEXTURE0 + *sampler_num);
102 glBindTexture(GL_TEXTURE_2D, texnum);
105 set_uniform_int(glsl_program_num, prefix, "dither_tex", *sampler_num);
108 // In theory, we should adjust for the texel centers that have moved here as well,
109 // but since we use GL_NEAREST and we don't really care a lot what texel we sample,
110 // we don't have to worry about it.
111 float tc_scale[] = { float(width) / float(texture_width), float(height) / float(texture_height) };
112 set_uniform_vec2(glsl_program_num, prefix, "tc_scale", tc_scale);