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Adds superficially correct compositeSampleLuminance8Phase8 function.

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Thereby uncovering a minor error in my decoding of colour phase.
This commit is contained in:
Thomas Harte 2020-08-10 21:33:59 -04:00
parent 525233e10b
commit 8374a5e579
3 changed files with 14 additions and 35 deletions
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2
OSBindings/Mac/Clock Signal.xcodeproj/xcshareddata/xcschemes/Clock Signal.xcscheme
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@ -67,7 +67,7 @@
</Testables>
</TestAction>
<LaunchAction
buildConfiguration = "Release"
buildConfiguration = "Debug"
selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
enableASanStackUseAfterReturn = "YES"

41
OSBindings/Mac/Clock Signal/ScanTarget/ScanTarget.metal
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@ -84,11 +84,11 @@ vertex SourceInterpolator scanToDisplay( constant Uniforms &uniforms [[buffer(1)
// Load up the colour details.
output.colourAmplitude = float(scans[instanceID].compositeAmplitude) / 255.0f;
output.colourPhase = mix(
output.colourPhase = 3.141592654f * mix(
float(scans[instanceID].endPoints[0].compositeAngle),
float(scans[instanceID].endPoints[1].compositeAngle),
float((vertexID&2) >> 1)
) / 64.0;
) / 32.0;
// Hence determine this quad's real shape, using vertexID to pick a corner.
output.position = float4(
@ -112,36 +112,6 @@ constexpr sampler standardSampler( coord::pixel,
// MARK: - Various input format conversion samplers.
/*
Luminance1, // 1 byte/pixel; any bit set => white; no bits set => black.
Luminance8, // 1 byte/pixel; linear scale.
PhaseLinkedLuminance8, // 4 bytes/pixel; each byte is an individual 8-bit luminance
// value and which value is output is a function of
// colour subcarrier phase — byte 0 defines the first quarter
// of each colour cycle, byte 1 the next quarter, etc. This
// format is intended to permit replay of sampled original data.
// The luminance plus phase types describe a luminance and the phase offset
// of a colour subcarrier. So they can be used to generate a luminance signal,
// or an s-video pipeline.
Luminance8Phase8, // 2 bytes/pixel; first is luminance, second is phase.
// Phase is encoded on a 192-unit circle; anything
// greater than 192 implies that the colour part of
// the signal should be omitted.
// The RGB types can directly feed an RGB pipeline, naturally, or can be mapped
// to phase+luminance, or just to luminance.
Red1Green1Blue1, // 1 byte/pixel; bit 0 is blue on or off, bit 1 is green, bit 2 is red.
Red2Green2Blue2, // 1 byte/pixel; bits 0 and 1 are blue, bits 2 and 3 are green, bits 4 and 5 are blue.
Red4Green4Blue4, // 2 bytes/pixel; first nibble is red, second is green, third is blue.
Red8Green8Blue8, // 4 bytes/pixel; first is red, second is green, third is blue, fourth is vacant.
*/
// There's only one meaningful way to sample the luminance formats.
fragment float4 sampleLuminance1(SourceInterpolator vert [[stage_in]], texture2d<ushort> texture [[texture(0)]]) {
@ -164,6 +134,13 @@ fragment float4 sampleLuminance8Phase8(SourceInterpolator vert [[stage_in]], tex
return float4(texture.sample(standardSampler, vert.textureCoordinates).rg, 0.0, 1.0);
}
fragment float4 compositeSampleLuminance8Phase8(SourceInterpolator vert [[stage_in]], texture2d<float> texture [[texture(0)]]) {
const auto luminancePhase = texture.sample(standardSampler, vert.textureCoordinates).rg;
const float phaseOffset = 3.141592654 * 4.0 * luminancePhase.g;
const float rawChroma = step(luminancePhase.g, 0.75) * cos(vert.colourPhase + phaseOffset);
return float4(float3(mix(luminancePhase.r, rawChroma, vert.colourAmplitude)), 1.0f);
}
// All the RGB formats can produce RGB, composite or S-Video.
fragment float4 sampleRed8Green8Blue8(SourceInterpolator vert [[stage_in]], texture2d<float> texture [[texture(0)]]) {

6
Outputs/ScanTarget.hpp
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@ -75,8 +75,10 @@ enum class InputDataType {
// of a colour subcarrier. So they can be used to generate a luminance signal,
// or an s-video pipeline.
Luminance8Phase8, // 2 bytes/pixel; first is luminance, second is phase.
// Phase is encoded on a 192-unit circle; anything
Luminance8Phase8, // 2 bytes/pixel; first is luminance, second is phase
// of a cosine wave.
//
// Phase is encoded on a 128-unit circle; anything
// greater than 192 implies that the colour part of
// the signal should be omitted.