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Starts a transition towards half-precision arithmetic.

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This commit is contained in:
Thomas Harte 2020-09-08 19:37:36 -04:00
parent 06b7ea5a6e
commit c82e0df071
2 changed files with 21 additions and 45 deletions
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28
OSBindings/Mac/Clock Signal/ScanTarget/CSScanTarget.mm
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@ -105,7 +105,7 @@ struct Uniforms {
float zoom;
simd::float2 offset;
simd::float3 chromaCoefficients[8];
float lumaKernel[8];
__fp16 lumaKernel[8];
float radiansPerPixel;
float cyclesMultiplier;
float outputAlpha;
@ -167,30 +167,6 @@ std::array<float, 8> boxCoefficients(float radiansPerPixel, float cutoff) {
return filter;
}
/// @returns the IEEE 754 binary16 conversion of @c value, stored in a 16-bit int.
uint16_t half(float value) {
uint16_t result = 0;
if(value < 0) {
result |= 0x8000;
value = -value;
}
int exponent;
const float mantissa = frexpf(value, &exponent);
// There is a bias of 15 on the exponent; given that the value given by frexp doesn't have the
// implicit first bit — that'll be masked off below — that's like a bias of 14 versus the output
// of frexp.
exponent += 14;
result |= (exponent & 31) << 10;
// Also store the mantissa.
result |= uint16_t(mantissa * 2048.0f) & 0x3ff;
return result;
}
}
using BufferingScanTarget = Outputs::Display::BufferingScanTarget;
@ -709,7 +685,7 @@ using BufferingScanTarget = Outputs::Display::BufferingScanTarget;
const auto coefficients = boxCoefficients(uniforms()->radiansPerPixel, 3.141592654f);
_lumaKernelSize = 15;
for(size_t c = 0; c < 8; ++c) {
filter[c] = coefficients[c];
filter[c] = __fp16(coefficients[c]);
if(coefficients[c] < 0.01f) {
_lumaKernelSize -= 2;
}

38
OSBindings/Mac/Clock Signal/ScanTarget/ScanTarget.metal
View File

@ -38,7 +38,7 @@ struct Uniforms {
// Describes the filter in use for luma filtering; 15 coefficients
// symmetrical around the centre.
float lumaKernel[8];
half lumaKernel[8];
// Maps from pixel offsets into the composition buffer to angular difference.
float radiansPerPixel;
@ -384,13 +384,13 @@ fragment float4 clearFragment() {
/// Given input pixels of the form (luminance, 0.5 + 0.5*chrominance*cos(phase), 0.5 + 0.5*chrominance*sin(phase)), applies a lowpass
/// filter to the two chrominance parts, then uses the toRGB matrix to convert to RGB and stores.
template <bool applyGamma> void filterChromaKernel( texture2d<float, access::read> inTexture [[texture(0)]],
texture2d<float, access::write> outTexture [[texture(1)]],
template <bool applyGamma> void filterChromaKernel( texture2d<half, access::read> inTexture [[texture(0)]],
texture2d<half, access::write> outTexture [[texture(1)]],
uint2 gid [[thread_position_in_grid]],
constant Uniforms &uniforms [[buffer(0)]],
constant int &offset [[buffer(1)]]) {
constexpr float4 moveToZero = float4(0.0f, 0.5f, 0.5f, 0.0f);
const float4 rawSamples[] = {
constexpr half4 moveToZero(0.0f, 0.5f, 0.5f, 0.0f);
const half4 rawSamples[] = {
inTexture.read(gid + uint2(0, offset)) - moveToZero,
inTexture.read(gid + uint2(1, offset)) - moveToZero,
inTexture.read(gid + uint2(2, offset)) - moveToZero,
@ -408,14 +408,14 @@ template <bool applyGamma> void filterChromaKernel( texture2d<float, access::rea
inTexture.read(gid + uint2(14, offset)) - moveToZero,
};
#define Sample(x, y) uniforms.chromaCoefficients[y] * rawSamples[x].rgb
const float3 colour =
#define Sample(x, y) half3(uniforms.chromaCoefficients[y]) * rawSamples[x].rgb
const half3 colour =
Sample(0, 0) + Sample(1, 1) + Sample(2, 2) + Sample(3, 3) + Sample(4, 4) + Sample(5, 5) + Sample(6, 6) +
Sample(7, 7) +
Sample(8, 6) + Sample(9, 5) + Sample(10, 4) + Sample(11, 3) + Sample(12, 2) + Sample(13, 1) + Sample(14, 0);
#undef Sample
const float4 output = float4(uniforms.toRGB * colour * uniforms.outputMultiplier, uniforms.outputAlpha);
const half4 output = half4(half3x3(uniforms.toRGB) * colour * half(uniforms.outputMultiplier), half(uniforms.outputAlpha));
if(applyGamma) {
outTexture.write(pow(output, uniforms.outputGamma), gid + uint2(7, offset));
} else {
@ -423,19 +423,19 @@ template <bool applyGamma> void filterChromaKernel( texture2d<float, access::rea
}
}
kernel void filterChromaKernelNoGamma(texture2d<float, access::read> inTexture [[texture(0)]],
texture2d<float, access::write> outTexture [[texture(1)]],
uint2 gid [[thread_position_in_grid]],
constant Uniforms &uniforms [[buffer(0)]],
constant int &offset [[buffer(1)]]) {
kernel void filterChromaKernelNoGamma( texture2d<half, access::read> inTexture [[texture(0)]],
texture2d<half, access::write> outTexture [[texture(1)]],
uint2 gid [[thread_position_in_grid]],
constant Uniforms &uniforms [[buffer(0)]],
constant int &offset [[buffer(1)]]) {
filterChromaKernel<false>(inTexture, outTexture, gid, uniforms, offset);
}
kernel void filterChromaKernelWithGamma(texture2d<float, access::read> inTexture [[texture(0)]],
texture2d<float, access::write> outTexture [[texture(1)]],
uint2 gid [[thread_position_in_grid]],
constant Uniforms &uniforms [[buffer(0)]],
constant int &offset [[buffer(1)]]) {
kernel void filterChromaKernelWithGamma( texture2d<half, access::read> inTexture [[texture(0)]],
texture2d<half, access::write> outTexture [[texture(1)]],
uint2 gid [[thread_position_in_grid]],
constant Uniforms &uniforms [[buffer(0)]],
constant int &offset [[buffer(1)]]) {
filterChromaKernel<true>(inTexture, outTexture, gid, uniforms, offset);
}
@ -473,7 +473,7 @@ kernel void separateLumaKernel( texture2d<half, access::read> inTexture [[textur
inTexture.read(gid + uint2(14, offset)).r,
};
#define Sample(x, y) half(uniforms.lumaKernel[y]) * rawSamples[x]
#define Sample(x, y) uniforms.lumaKernel[y] * rawSamples[x]
const half luminance =
Sample(0, 0) + Sample(1, 1) + Sample(2, 2) + Sample(3, 3) + Sample(4, 4) + Sample(5, 5) + Sample(6, 6) +
Sample(7, 7) +