Make the dither effect cheat a small bit and use a repeating dither texture no greate...

[movit] / dither_effect.cpp

diff --git a/dither_effect.cpp b/dither_effect.cpp
index cdfb157e675900a08ed3a859889641e01df7ba4a..87e729a3c9feca0a7253e7617eeb41d287d9f68b 100644 (file)
--- a/dither_effect.cpp
+++ b/dither_effect.cpp
@@ -47,11 +47,17 @@ void DitherEffect::update_texture(GLuint glsl_program_num, const std::string &pr
        float *dither_noise = new float[width * height];
        float dither_double_amplitude = 1.0f / (1 << num_bits);
 
+       // We don't need a strictly nonrepeating dither; reducing the resolution
+       // to max 128x128 saves a lot of texture bandwidth, without causing any
+       // noticeable harm to the dither's performance.
+       texture_width = std::min(width, 128);
+       texture_height = std::min(height, 128);
+
        // 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) {
+       for (int i = 0; i < texture_width * texture_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;
@@ -63,11 +69,13 @@ void DitherEffect::update_texture(GLuint glsl_program_num, const std::string &pr
        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);
+       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+       check_error();
+       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
        check_error();
-       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
        check_error();
-       glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE16F_ARB, width, height, 0, GL_LUMINANCE, GL_FLOAT, dither_noise);
+       glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE16F_ARB, texture_width, texture_height, 0, GL_LUMINANCE, GL_FLOAT, dither_noise);
        check_error();
 
        delete[] dither_noise;
@@ -91,4 +99,10 @@ void DitherEffect::set_gl_state(GLuint glsl_program_num, const std::string &pref
 
        set_uniform_int(glsl_program_num, prefix, "dither_tex", *sampler_num);
        ++sampler_num;
+
+       // In theory, we should adjust for the texel centers that have moved here as well,
+       // but since we use GL_NEAREST and we don't really care a lot what texel we sample,
+       // we don't have to worry about it.     
+       float tc_scale[] = { float(width) / float(texture_width), float(height) / float(texture_height) };
+       set_uniform_vec2(glsl_program_num, prefix, "tc_scale", tc_scale);
 }