renderer/cm: higher-quality tonemapping (#12204)

4 files changed, 32 insertions, 25 deletions

diff --git a/src/render/OpenGL.cpp b/src/render/OpenGL.cpp
index 19c07923..2f1bccb2 100644
--- a/src/render/OpenGL.cpp
+++ b/src/render/OpenGL.cpp
@@ -971,6 +971,7 @@ static void getCMShaderUniforms(SShader& shader) {
     shader.uniformLocations[SHADER_DST_TF_RANGE]      = glGetUniformLocation(shader.program, "dstTFRange");
     shader.uniformLocations[SHADER_TARGET_PRIMARIES]  = glGetUniformLocation(shader.program, "targetPrimaries");
     shader.uniformLocations[SHADER_MAX_LUMINANCE]     = glGetUniformLocation(shader.program, "maxLuminance");
+    shader.uniformLocations[SHADER_SRC_REF_LUMINANCE] = glGetUniformLocation(shader.program, "srcRefLuminance");
     shader.uniformLocations[SHADER_DST_MAX_LUMINANCE] = glGetUniformLocation(shader.program, "dstMaxLuminance");
     shader.uniformLocations[SHADER_DST_REF_LUMINANCE] = glGetUniformLocation(shader.program, "dstRefLuminance");
     shader.uniformLocations[SHADER_SDR_SATURATION]    = glGetUniformLocation(shader.program, "sdrSaturation");
@@ -1560,6 +1561,14 @@ static bool isSDR2HDR(const NColorManagement::SImageDescription& imageDescriptio
          targetImageDescription.transferFunction == NColorManagement::CM_TRANSFER_FUNCTION_HLG);
 }
 
+static bool isHDR2SDR(const NColorManagement::SImageDescription& imageDescription, const NColorManagement::SImageDescription& targetImageDescription) {
+    // might be too strict
+    return (imageDescription.transferFunction == NColorManagement::CM_TRANSFER_FUNCTION_ST2084_PQ ||
+            imageDescription.transferFunction == NColorManagement::CM_TRANSFER_FUNCTION_HLG) &&
+        (targetImageDescription.transferFunction == NColorManagement::CM_TRANSFER_FUNCTION_SRGB ||
+         targetImageDescription.transferFunction == NColorManagement::CM_TRANSFER_FUNCTION_GAMMA22);
+}
+
 void CHyprOpenGLImpl::passCMUniforms(SShader& shader, const NColorManagement::SImageDescription& imageDescription,
                                      const NColorManagement::SImageDescription& targetImageDescription, bool modifySDR, float sdrMinLuminance, int sdrMaxLuminance) {
     static auto PSDREOTF = CConfigValue<Hyprlang::INT>("render:cm_sdr_eotf");
@@ -1585,16 +1594,22 @@ void CHyprOpenGLImpl::passCMUniforms(SShader& shader, const NColorManagement::SI
     shader.setUniformMatrix4x2fv(SHADER_TARGET_PRIMARIES, 1, false, glTargetPrimaries);
 
     const bool needsSDRmod = modifySDR && isSDR2HDR(imageDescription, targetImageDescription);
+    const bool needsHDRmod = !needsSDRmod && isHDR2SDR(imageDescription, targetImageDescription);
 
     shader.setUniformFloat2(SHADER_SRC_TF_RANGE, imageDescription.getTFMinLuminance(needsSDRmod ? sdrMinLuminance : -1),
                             imageDescription.getTFMaxLuminance(needsSDRmod ? sdrMaxLuminance : -1));
     shader.setUniformFloat2(SHADER_DST_TF_RANGE, targetImageDescription.getTFMinLuminance(needsSDRmod ? sdrMinLuminance : -1),
                             targetImageDescription.getTFMaxLuminance(needsSDRmod ? sdrMaxLuminance : -1));
 
-    const float maxLuminance = imageDescription.luminances.max > 0 ? imageDescription.luminances.max : imageDescription.luminances.reference;
-    shader.setUniformFloat(SHADER_MAX_LUMINANCE, maxLuminance * targetImageDescription.luminances.reference / imageDescription.luminances.reference);
+    shader.setUniformFloat(SHADER_SRC_REF_LUMINANCE, imageDescription.getTFRefLuminance(-1));
+    shader.setUniformFloat(SHADER_DST_REF_LUMINANCE, targetImageDescription.getTFRefLuminance(-1));
+
+    const float maxLuminance =
+        needsHDRmod ? imageDescription.getTFMaxLuminance(-1) : (imageDescription.luminances.max > 0 ? imageDescription.luminances.max : imageDescription.luminances.reference);
+    shader.setUniformFloat(SHADER_MAX_LUMINANCE,
+                           maxLuminance * targetImageDescription.luminances.reference /
+                               (needsHDRmod ? imageDescription.getTFRefLuminance(-1) : imageDescription.luminances.reference));
     shader.setUniformFloat(SHADER_DST_MAX_LUMINANCE, targetImageDescription.luminances.max > 0 ? targetImageDescription.luminances.max : 10000);
-    shader.setUniformFloat(SHADER_DST_REF_LUMINANCE, targetImageDescription.luminances.reference);
     shader.setUniformFloat(SHADER_SDR_SATURATION, needsSDRmod && m_renderData.pMonitor->m_sdrSaturation > 0 ? m_renderData.pMonitor->m_sdrSaturation : 1.0f);
     shader.setUniformFloat(SHADER_SDR_BRIGHTNESS, needsSDRmod && m_renderData.pMonitor->m_sdrBrightness > 0 ? m_renderData.pMonitor->m_sdrBrightness : 1.0f);
     const auto cacheKey = std::make_pair(imageDescription.getId(), targetImageDescription.getId());
@@ -1710,11 +1725,8 @@ void CHyprOpenGLImpl::renderTextureInternal(SP<CTexture> tex, const CBox& box, c
     if (shader == &m_shaders->m_shCM) {
         shader->setUniformInt(SHADER_TEX_TYPE, texType);
         if (data.cmBackToSRGB) {
-            // revert luma changes to avoid black screenshots.
-            // this will likely not be 1:1, and might cause screenshots to be too bright, but it's better than pitch black.
-            imageDescription.luminances = {};
-            static auto PSDREOTF        = CConfigValue<Hyprlang::INT>("render:cm_sdr_eotf");
-            auto        chosenSdrEotf   = *PSDREOTF > 0 ? NColorManagement::CM_TRANSFER_FUNCTION_GAMMA22 : NColorManagement::CM_TRANSFER_FUNCTION_SRGB;
+            static auto PSDREOTF      = CConfigValue<Hyprlang::INT>("render:cm_sdr_eotf");
+            auto        chosenSdrEotf = *PSDREOTF > 0 ? NColorManagement::CM_TRANSFER_FUNCTION_GAMMA22 : NColorManagement::CM_TRANSFER_FUNCTION_SRGB;
             passCMUniforms(*shader, imageDescription, NColorManagement::SImageDescription{.transferFunction = chosenSdrEotf}, true, -1, -1);
         } else
             passCMUniforms(*shader, imageDescription);
diff --git a/src/render/Shader.hpp b/src/render/Shader.hpp
index 4f545642..50ff5889 100644
--- a/src/render/Shader.hpp
+++ b/src/render/Shader.hpp
@@ -16,6 +16,7 @@ enum eShaderUniform : uint8_t {
     SHADER_DST_TF_RANGE,
     SHADER_TARGET_PRIMARIES,
     SHADER_MAX_LUMINANCE,
+    SHADER_SRC_REF_LUMINANCE,
     SHADER_DST_MAX_LUMINANCE,
     SHADER_DST_REF_LUMINANCE,
     SHADER_SDR_SATURATION,
diff --git a/src/render/shaders/glsl/CM.glsl b/src/render/shaders/glsl/CM.glsl
index 0e79aab0..362d7cfb 100644
--- a/src/render/shaders/glsl/CM.glsl
+++ b/src/render/shaders/glsl/CM.glsl
@@ -2,6 +2,7 @@ uniform vec2 srcTFRange;
 uniform vec2 dstTFRange;
 
 uniform float maxLuminance;
+uniform float srcRefLuminance;
 uniform float dstMaxLuminance;
 uniform float dstRefLuminance;
 uniform float sdrSaturation;
@@ -387,24 +388,17 @@ vec4 tonemap(vec4 color, mat3 dstXYZ) {
         PQ_INV_M1
     ) * HDR_MAX_LUMINANCE;
 
-    float srcScale = maxLuminance / dstRefLuminance;
-    float dstScale = dstMaxLuminance / dstRefLuminance;
+    float linearPart = min(luminance, dstRefLuminance);
+    float luminanceAboveRef = max(luminance - dstRefLuminance, 0.0);
+    float maxExcessLuminance = max(maxLuminance - dstRefLuminance, 1.0);
+    float shoulder = log((luminanceAboveRef / maxExcessLuminance + 1.0) * (M_E - 1.0));
+    float mappedHigh = shoulder * (dstMaxLuminance - dstRefLuminance);
+    float newLum = clamp(linearPart + mappedHigh, 0.0, dstMaxLuminance);
 
-    float minScale = min(srcScale, 1.5);
-    float dimming = 1.0 / clamp(minScale / dstScale, 1.0, minScale);
-    float refLuminance = dstRefLuminance * dimming;
+    // scale src to dst reference
+    float refScale = dstRefLuminance / srcRefLuminance;
 
-    float low = min(luminance * dimming, refLuminance);
-    float highlight = clamp((luminance / dstRefLuminance - 1.0) / (srcScale - 1.0), 0.0, 1.0);
-    float high = log(highlight * (M_E - 1.0) + 1.0) * (dstMaxLuminance - refLuminance);
-    luminance = low + high;
-
-    E = pow(clamp(ICtCp[0], 0.0, 1.0), PQ_M1);
-    ICtCp[0] = pow(
-        (PQ_C1 + PQ_C2 * E) / (1.0 + PQ_C3 * E),
-        PQ_M2
-    ) / HDR_MAX_LUMINANCE;
-    return vec4(fromLMS * toLinear(vec4(ICtCpPQInv * ICtCp, 1.0), CM_TRANSFER_FUNCTION_ST2084_PQ).rgb * HDR_MAX_LUMINANCE, color[3]);
+    return vec4(fromLMS * toLinear(vec4(ICtCpPQInv * ICtCp, 1.0), CM_TRANSFER_FUNCTION_ST2084_PQ).rgb * HDR_MAX_LUMINANCE * refScale, color[3]); 
 }
 
 vec4 doColorManagement(vec4 pixColor, int srcTF, int dstTF, mat4x2 dstPrimaries) {
diff --git a/src/render/shaders/glsl/blurprepare.frag b/src/render/shaders/glsl/blurprepare.frag
index 548289c3..6b9809f8 100644
--- a/src/render/shaders/glsl/blurprepare.frag
+++ b/src/render/shaders/glsl/blurprepare.frag
@@ -28,7 +28,7 @@ void main() {
             pixColor.rgb /= sdrBrightnessMultiplier;
         }
         pixColor.rgb = convertMatrix * toLinearRGB(pixColor.rgb, sourceTF);
-        pixColor = toNit(pixColor, srcTFRange);
+        pixColor = toNit(pixColor, vec2(srcTFRange[0], srcRefLuminance));
         pixColor = fromLinearNit(pixColor, targetTF, dstTFRange);
     }