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Made an attempt intelligently to use bilinear filtering to increase filtering quality with the same number of samples.

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This commit is contained in:
Thomas Harte 2016-04-29 18:37:35 -04:00
parent 501ab74eaf
commit 16ef09fc2b
4 changed files with 62 additions and 19 deletions
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2
Outputs/CRT/Internals/CRTOpenGL.cpp
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@ -533,7 +533,7 @@ void OpenGLOutputBuilder::set_timing_uniforms()
}
float colour_subcarrier_frequency = (float)_colour_cycle_numerator / (float)_colour_cycle_denominator;
if(composite_y_filter_shader_program) composite_y_filter_shader_program->set_filter_coefficients(_cycles_per_line, colour_subcarrier_frequency * 0.5f);
if(composite_y_filter_shader_program) composite_y_filter_shader_program->set_filter_coefficients(_cycles_per_line, colour_subcarrier_frequency - 90.0f);
if(composite_chrominance_filter_shader_program) composite_chrominance_filter_shader_program->set_filter_coefficients(_cycles_per_line, colour_subcarrier_frequency * 0.5f);
_output_mutex->unlock();
}

74
Outputs/CRT/Internals/Shaders/IntermediateShader.cpp
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@ -44,6 +44,7 @@ std::unique_ptr<IntermediateShader> IntermediateShader::make_shader(const char *
"uniform ivec2 outputTextureSize;"
"uniform float extension;"
"uniform %s texID;"
"uniform float offsets[5];"
"out vec2 phaseAndAmplitudeVarying;"
"out vec2 inputPositionsVarying[11];"
@ -60,17 +61,17 @@ std::unique_ptr<IntermediateShader> IntermediateShader::make_shader(const char *
"iInputPositionVarying = extendedInputPosition;"
"vec2 mappedInputPosition = (extendedInputPosition + vec2(0.0, 0.5)) / textureSize;"
"inputPositionsVarying[0] = mappedInputPosition - (vec2(10.0, 0.0) / textureSize);"
"inputPositionsVarying[1] = mappedInputPosition - (vec2(8.0, 0.0) / textureSize);"
"inputPositionsVarying[2] = mappedInputPosition - (vec2(6.0, 0.0) / textureSize);"
"inputPositionsVarying[3] = mappedInputPosition - (vec2(4.0, 0.0) / textureSize);"
"inputPositionsVarying[4] = mappedInputPosition - (vec2(2.0, 0.0) / textureSize);"
"inputPositionsVarying[0] = mappedInputPosition - (vec2(offsets[4], 0.0) / textureSize);"
"inputPositionsVarying[1] = mappedInputPosition - (vec2(offsets[3], 0.0) / textureSize);"
"inputPositionsVarying[2] = mappedInputPosition - (vec2(offsets[2], 0.0) / textureSize);"
"inputPositionsVarying[3] = mappedInputPosition - (vec2(offsets[1], 0.0) / textureSize);"
"inputPositionsVarying[4] = mappedInputPosition - (vec2(offsets[0], 0.0) / textureSize);"
"inputPositionsVarying[5] = mappedInputPosition;"
"inputPositionsVarying[6] = mappedInputPosition + (vec2(2.0, 0.0) / textureSize);"
"inputPositionsVarying[7] = mappedInputPosition + (vec2(4.0, 0.0) / textureSize);"
"inputPositionsVarying[8] = mappedInputPosition + (vec2(6.0, 0.0) / textureSize);"
"inputPositionsVarying[9] = mappedInputPosition + (vec2(8.0, 0.0) / textureSize);"
"inputPositionsVarying[10] = mappedInputPosition + (vec2(10.0, 0.0) / textureSize);"
"inputPositionsVarying[6] = mappedInputPosition + (vec2(offsets[0], 0.0) / textureSize);"
"inputPositionsVarying[7] = mappedInputPosition + (vec2(offsets[1], 0.0) / textureSize);"
"inputPositionsVarying[8] = mappedInputPosition + (vec2(offsets[2], 0.0) / textureSize);"
"inputPositionsVarying[9] = mappedInputPosition + (vec2(offsets[3], 0.0) / textureSize);"
"inputPositionsVarying[10] = mappedInputPosition + (vec2(offsets[4], 0.0) / textureSize);"
"delayLinePositionVarying = mappedInputPosition - vec2(0.0, 1.0);"
"phaseAndAmplitudeVarying.x = (phaseCyclesPerTick * (extendedOutputPosition.x - phaseTime) + phaseAmplitudeAndOffset.x) * 2.0 * 3.141592654;"
@ -90,6 +91,7 @@ std::unique_ptr<IntermediateShader> IntermediateShader::make_shader(const char *
shader->weightsUniform = shader->get_uniform_location("weights");
shader->rgbToLumaChromaUniform = shader->get_uniform_location("rgbToLumaChroma");
shader->lumaChromaToRGBUniform = shader->get_uniform_location("lumaChromaToRGB");
shader->offsetsUniform = shader->get_uniform_location("offsets");
return shader;
}
@ -264,14 +266,54 @@ void IntermediateShader::set_filter_coefficients(float sampling_rate, float cuto
{
bind();
sampling_rate *= 0.5f;
cutoff_frequency *= 0.5f;
// The process below: the source texture will have bilinear filtering enabled; so by
// sampling at non-integral offsets from the centre the shader can get a weighted sum
// of two source pixels, then scale that once, to do two taps per sample. However
// that works only if the two coefficients being joined have the same sign. So the
// number of usable taps is between 11 and 21 depending on the values that come out.
// Perform a linear search for the highest number of taps we can use with 11 samples.
float weights[12];
weights[11] = 0.0f;
SignalProcessing::FIRFilter luminance_filter(11, sampling_rate, 0.0f, cutoff_frequency, SignalProcessing::FIRFilter::DefaultAttenuation);
luminance_filter.get_coefficients(weights);
float offsets[5];
unsigned int taps = 21;
while(1)
{
float coefficients[21];
SignalProcessing::FIRFilter luminance_filter(taps, sampling_rate, 0.0f, cutoff_frequency, SignalProcessing::FIRFilter::DefaultAttenuation);
luminance_filter.get_coefficients(coefficients);
int sample = 0;
int c = 0;
memset(weights, 0, sizeof(float)*12);
while(c < (taps >> 1) && sample < 5)
{
if((coefficients[c] < 0.0f) == (coefficients[c+1] < 0.0f) && c+1 < (taps >> 1))
{
weights[sample] = coefficients[c] + coefficients[c+1];
offsets[sample] = (float)c + 1.0f + (coefficients[c+1] / weights[sample]);
c += 2;
}
else
{
offsets[sample] = (float)c + 1.0f;
weights[sample] = coefficients[c];
c++;
}
sample ++;
}
if(c == (taps >> 1))
{
weights[sample] = coefficients[c];
for(int c = 0; c < sample; c++)
{
weights[sample+c+1] = weights[sample-c-1];
}
break;
}
taps -= 2;
}
glUniform4fv(weightsUniform, 3, weights);
glUniform1fv(offsetsUniform, 5, offsets);
}
void IntermediateShader::set_phase_cycles_per_sample(float phase_cycles_per_sample, bool extend_runs_to_full_cycle)

1
Outputs/CRT/Internals/Shaders/IntermediateShader.hpp
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@ -74,6 +74,7 @@ private:
GLint extensionUniform;
GLint rgbToLumaChromaUniform;
GLint lumaChromaToRGBUniform;
GLint offsetsUniform;
};
}

4
Outputs/CRT/Internals/TextureTarget.cpp
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@ -18,8 +18,8 @@ TextureTarget::TextureTarget(GLsizei width, GLsizei height) : _width(width), _he
glGenTextures(1, &_texture);
glBindTexture(GL_TEXTURE_2D, _texture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, (GLsizei)width, (GLsizei)height, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, _texture, 0);