Fixed primary transforms for wide colour gamut systems such as HDR breaking the mask and resulting in muddy colours

hdr/shaders/crt-sony-megatron-hdr-pass.slang

@@ -23,6 +23,7 @@ Dont use this shader directly - use the hdr\crt-make-model-hdr.slangp where make
 THIS SHADER DOES NOT SUPPORT WRGB OLED (Due to the sub pixel layout of WRGB - RGB QD-OLED or LCD (and variants thereof screens are fine)
 */
 
+//#pragma format A2B10G10R10_UNORM_PACK32
 #pragma format R16G16B16A16_SFLOAT
 
 layout(push_constant) uniform Push
@@ -31,6 +32,7 @@ layout(push_constant) uniform Push
    float hcrt_hdr;
    float hcrt_max_nits;
    float hcrt_paper_white_nits;
+   float hcrt_expand_gamut;
 } params;
 
 layout(std140, set = 0, binding = 0) uniform UBO
@@ -47,6 +49,7 @@ layout(std140, set = 0, binding = 0) uniform UBO
 #define HCRT_HDR                            params.hcrt_hdr
 #define HCRT_MAX_NITS                       params.hcrt_max_nits
 #define HCRT_PAPER_WHITE_NITS               params.hcrt_paper_white_nits
+#define HCRT_EXPAND_GAMUT                   params.hcrt_expand_gamut
 
 #define COMPAT_TEXTURE(c, d) texture(c, d)
 
@@ -67,6 +70,7 @@ layout(location = 0) out vec4 FragColor;
 layout(set = 0, binding = 2) uniform sampler2D Source;
 
 #include "include/inverse_tonemap.h"
+#include "include/hdr10.h"
 
 vec3 InverseTonemapConditional(const vec3 linear)
 {
@@ -84,7 +88,19 @@ void main()
 {
    vec3 source = COMPAT_TEXTURE(Source, vTexCoord).rgb;
 
-   const vec3 hdr_colour   = InverseTonemapConditional(source);
+   vec3 hdr_colour   = InverseTonemapConditional(source);
 
-   FragColor = vec4(hdr_colour, 1.0);
+   vec3 transformed_colour;
+
+   if(HCRT_HDR < 1.0f)
+   {      
+      transformed_colour = hdr_colour;
+   }
+   else
+   {
+      const vec3 rec2020  = hdr_colour * k2020Gamuts[uint(HCRT_EXPAND_GAMUT)];
+      transformed_colour  = rec2020 * (HCRT_PAPER_WHITE_NITS / kMaxNitsFor2084);
+   }
+
+   FragColor = vec4(transformed_colour, 1.0);
 }

hdr/shaders/crt-sony-megatron-source-pass.slang

@@ -88,5 +88,23 @@ void main()
 
    const vec3 colour   = ColourGrade(source);
 
-   FragColor = vec4(colour, 1.0);
+   vec3 transformed_colour;
+
+   if(HCRT_HDR < 1.0f)
+   {
+      if(HCRT_OUTPUT_COLOUR_SPACE == 2.0f)
+      {
+         transformed_colour = (colour * k709_to_XYZ) * kXYZ_to_DCIP3; 
+      }
+      else
+      {
+         transformed_colour = colour;
+      }
+   }
+   else
+   {
+      transformed_colour = colour;
+   }
+
+   FragColor = vec4(transformed_colour, 1.0);
 }

hdr/shaders/crt-sony-megatron.slang

@@ -1124,7 +1124,6 @@ const uint kBlackWhiteMasks[kResolutionAxis][kTVLAxis][kBGRAxis][kMaxBlackWhiteS
 #endif // ENABLE_BLACK_WHITE_MASKS
 
 #include "include/scanline_generation.h"
-#include "include/hdr10.h"
 #include "include/gamma_correct.h"
 
 #define k1080p     0
@@ -1635,9 +1634,9 @@ void main()
       scanline_colour += scanline_channel_2 * kColourMask[channel_2];
    }
 
-   vec3 hdr10; 
+   vec3 gamma_corrected; 
    
-   GammaCorrect(scanline_colour, hdr10);
+   GammaCorrect(scanline_colour, gamma_corrected);
 
-   FragColor = vec4(hdr10, 1.0f);
+   FragColor = vec4(gamma_corrected, 1.0f);
 }

hdr/shaders/include/colour_grade.h

@@ -27,6 +27,11 @@ const mat3 kXYZ_to_709 = mat3(
    -0.969244f,  1.875968f,  0.041555f,
     0.055630f, -0.203977f,  1.056972f);
 
+const mat3 kXYZ_to_DCIP3 = mat3 (
+    2.4934969119f, -0.9313836179f, -0.4027107845f,
+   -0.8294889696f,  1.7626640603f,  0.0236246858f,
+    0.0358458302f, -0.0761723893f,  0.9568845240f);   
+
 const mat3 kColourGamut[kColourSystems] = { k709_to_XYZ, kPAL_to_XYZ, kNTSC_to_XYZ, kNTSC_to_XYZ };
 
 const float kTemperatures[kColourSystems] = { kD65, kD65, kD65, kD93 }; 

hdr/shaders/include/gamma_correct.h

@@ -1,3 +1,5 @@
+#include "hdr10.h"
+
 // SDR Colour output spaces
 
 const mat3 k709_to_XYZ = mat3(
@@ -40,26 +42,25 @@ vec3 LinearToDCIP3(const vec3 colour)
 	return vec3(LinearToDCIP3_1(colour.r), LinearToDCIP3_1(colour.g), LinearToDCIP3_1(colour.b));
 }
 
-void GammaCorrect(const vec3 scanline_colour, inout vec3 gamma_out)
+void GammaCorrect(const vec3 scanline_colour, inout vec3 gamma_corrected)
 {
    if(HCRT_HDR < 1.0f)
    {
       if(HCRT_OUTPUT_COLOUR_SPACE == 0.0f)
       {
-         gamma_out = LinearTo709(scanline_colour);
+         gamma_corrected = LinearTo709(scanline_colour);
       }
       else if(HCRT_OUTPUT_COLOUR_SPACE == 1.0f)
       {
-         gamma_out = LinearTosRGB(scanline_colour);
+         gamma_corrected = LinearTosRGB(scanline_colour);
       }
       else
       {
-         const vec3 dcip3_colour = (scanline_colour * k709_to_XYZ) * kXYZ_to_DCIP3; 
-         gamma_out = LinearToDCIP3(dcip3_colour);
+         gamma_corrected = LinearToDCIP3(scanline_colour);
       }
    }
    else
    {
-      gamma_out = Hdr10(scanline_colour, HCRT_PAPER_WHITE_NITS, HCRT_EXPAND_GAMUT);
+      gamma_corrected = LinearToST2084(scanline_colour);
    }
 }

hdr/shaders/include/hdr10.h

@@ -14,19 +14,25 @@ const mat3 kExpanded709_to_2020 = mat3 (
 
 const mat3 k2020Gamuts[2] = { k709_to_2020, kExpanded709_to_2020 };
 
-vec3 LinearToST2084(vec3 normalizedLinearValue)
+float LinearToST2084_1(const float channel)
 {
-   vec3 ST2084 = pow((0.8359375f + 18.8515625f * pow(abs(normalizedLinearValue), vec3(0.1593017578f))) / (1.0f + 18.6875f * pow(abs(normalizedLinearValue), vec3(0.1593017578f))), vec3(78.84375f));
+   float ST2084 = pow((0.8359375f + 18.8515625f * pow(abs(channel), 0.1593017578f)) / (1.0f + 18.6875f * pow(abs(channel), 0.1593017578f)), 78.84375f);
    return ST2084;  /* Don't clamp between [0..1], so we can still perform operations on scene values higher than 10,000 nits */
 }
+
+vec3 LinearToST2084(const vec3 colour)
+{
+	return vec3(LinearToST2084_1(colour.r), LinearToST2084_1(colour.g), LinearToST2084_1(colour.b));
+}
+
 /* END Converted from (Copyright (c) Microsoft Corporation - Licensed under the MIT License.)  https://github.com/microsoft/Xbox-ATG-Samples/tree/master/Kits/ATGTK/HDR */
 
 /* Convert into HDR10 */
-vec3 Hdr10(vec3 hdr_linear, float paper_white_nits, float expand_gamut)
+vec3 Hdr10(const vec3 hdr_linear, float paper_white_nits, float expand_gamut)
 {
-   vec3 rec2020       = hdr_linear * k2020Gamuts[uint(expand_gamut)];
-   vec3 linearColour  = rec2020 * (paper_white_nits / kMaxNitsFor2084);
-   vec3 hdr10         = LinearToST2084(linearColour);
+   const vec3 rec2020       = hdr_linear * k2020Gamuts[uint(expand_gamut)];
+   const vec3 linearColour  = rec2020 * (paper_white_nits / kMaxNitsFor2084);
+   vec3 hdr10               = LinearToST2084(linearColour);
 
    return hdr10;
 }