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Fix HDR10 swapchain encoding by adding missing bt2020 color space conversion #3

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Fix HDR10 swapchain encoding by adding missing bt2020 color space conversion #3

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17fe433
Add bt709/bt2020 conversion matrices
NotVoosh Feb 28, 2026
02668e0
Fix HDR10 swapchain color space encoding/decoding
NotVoosh Feb 28, 2026
d08fe02
Fix broken compilation
NotVoosh Mar 1, 2026
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35 changes: 35 additions & 0 deletions Shaders/smolbbsoop/smolbbsoop_Global.fxh
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Original file line number Diff line number Diff line change
Expand Up @@ -89,6 +89,41 @@
ui_tooltip = "Input HDR Peak Brightness. Setting the correct value ensures the conversion is as accurate as possible";
> = 1000;

//============================================================================================
// Color Spaces Conversion Matrices and Functions
// From https://github.com/clshortfuse/renodx/tree/main/src/shaders
//============================================================================================

static const float3x3 BT709_TO_XYZ_MAT = float3x3(
0.4123907993f, 0.3575843394f, 0.1804807884f,
0.2126390059f, 0.7151686788f, 0.0721923154f,
0.0193308187f, 0.1191947798f, 0.9505321522f);

static const float3x3 XYZ_TO_BT709_MAT = float3x3(
3.2409699419f, -1.5373831776f, -0.4986107603f,
-0.9692436363f, 1.8759675015f, 0.0415550574f,
0.0556300797f, -0.2039769589f, 1.0569715142f);

static const float3x3 BT2020_TO_XYZ_MAT = float3x3(
0.6369580483f, 0.1446169036f, 0.1688809752f,
0.2627002120f, 0.6779980715f, 0.0593017165f,
0.0000000000f, 0.0280726930f, 1.0609850577f);

static const float3x3 XYZ_TO_BT2020_MAT = float3x3(
1.7166511880f, -0.3556707838f, -0.2533662814f,
-0.6666843518f, 1.6164812366f, 0.0157685458f,
0.0176398574f, -0.0427706133f, 0.9421031212f);

//static const float3x3 BT709_TO_BT2020_MAT = mul(XYZ_TO_BT2020_MAT, BT709_TO_XYZ_MAT);
//static const float3x3 BT2020_TO_BT709_MAT = mul(XYZ_TO_BT709_MAT, BT2020_TO_XYZ_MAT);

float3 Bt709FromBt2020(float3 bt2020){
return mul(mul(XYZ_TO_BT709_MAT, BT2020_TO_XYZ_MAT), bt2020);
}
float3 Bt2020FromBt709(float3 bt709){
return mul(mul(XYZ_TO_BT2020_MAT, BT709_TO_XYZ_MAT), bt709);
}

//==============================================================
// Functions (After)
//==============================================================
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9 changes: 5 additions & 4 deletions Shaders/smolbbsoop_HDR_Converter.fx
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Original file line number Diff line number Diff line change
Expand Up @@ -101,10 +101,11 @@ SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
float4 ConvertBufferBefore(float4 pos : SV_Position, float2 texcoord : TEXCOORD) : SV_Target
{
float3 HDRColour = tex2D(ReShade::BackBuffer, texcoord).rgb;
float3 LinearColour = PQToLinear(HDRColour.rgb);
float3 LinearBt2020Colour = PQToLinear(HDRColour.rgb);
float3 LinearBt709Colour = Bt2020FromBt709(LinearBt2020Colour);

// Apply tonemap in linear space, then convert to sRGB
float3 TonemappedLinear = Reinhard(LinearColour);
float3 TonemappedLinear = Reinhard(LinearBt709Colour);
float3 sRGBColour = LinearTosRGB(TonemappedLinear);

return float4(sRGBColour, 1.0);
Expand All @@ -121,8 +122,8 @@ SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
// Convert to linear, then inverse tonemap
float3 LinearColour = sRGBToLinear(sRGBColour);
float3 InvTonemappedLinear = InvReinhard(LinearColour);

float3 HDRColour = LinearToPQ(InvTonemappedLinear);
float3 LinearBt2020Colour = Bt709FromBt2020(InvTonemappedLinear);
float3 HDRColour = LinearToPQ(LinearBt2020Colour);

return float4(HDRColour, 1.0);
}
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