From 148241117bd67c11dba2c00096dd56a8e984e07d Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Thu, 23 Jul 2026 08:09:02 -0700
Subject: [PATCH] Define SCRGB_NITS for use in HDR color calculations
---
src/render/SDL_render.c | 4 ++--
src/render/direct3d11/SDL_render_d3d11.c | 6 +++---
src/render/direct3d12/SDL_render_d3d12.c | 6 +++---
src/render/vulkan/SDL_render_vulkan.c | 6 +++---
src/video/SDL_pixels_c.h | 2 ++
src/video/windows/SDL_windowsmodes.c | 3 ++-
test/testcolorspace.c | 7 +++++--
7 files changed, 20 insertions(+), 14 deletions(-)
diff --git a/src/render/SDL_render.c b/src/render/SDL_render.c
index 8d441e317cfd1..9dbb2739dac19 100644
--- a/src/render/SDL_render.c
+++ b/src/render/SDL_render.c
@@ -5448,7 +5448,7 @@ SDL_Surface *SDL_RenderReadPixels(SDL_Renderer *renderer, const SDL_Rect *rect)
SDL_PixelFormat expected_format = (parent ? parent->format : target->format);
if (SDL_COLORSPACETRANSFER(target->colorspace) == SDL_TRANSFER_CHARACTERISTICS_PQ) {
- SDL_SetFloatProperty(props, SDL_PROP_SURFACE_SDR_WHITE_POINT_FLOAT, target->SDR_white_point * 80.0f);
+ SDL_SetFloatProperty(props, SDL_PROP_SURFACE_SDR_WHITE_POINT_FLOAT, target->SDR_white_point * SCRGB_NITS);
} else {
SDL_SetFloatProperty(props, SDL_PROP_SURFACE_SDR_WHITE_POINT_FLOAT, target->SDR_white_point);
}
@@ -5464,7 +5464,7 @@ SDL_Surface *SDL_RenderReadPixels(SDL_Renderer *renderer, const SDL_Rect *rect)
}
} else {
if (SDL_COLORSPACETRANSFER(renderer->output_colorspace) == SDL_TRANSFER_CHARACTERISTICS_PQ) {
- SDL_SetFloatProperty(props, SDL_PROP_SURFACE_SDR_WHITE_POINT_FLOAT, renderer->SDR_white_point * 80.0f);
+ SDL_SetFloatProperty(props, SDL_PROP_SURFACE_SDR_WHITE_POINT_FLOAT, renderer->SDR_white_point * SCRGB_NITS);
} else {
SDL_SetFloatProperty(props, SDL_PROP_SURFACE_SDR_WHITE_POINT_FLOAT, renderer->SDR_white_point);
}
diff --git a/src/render/direct3d11/SDL_render_d3d11.c b/src/render/direct3d11/SDL_render_d3d11.c
index 9e775ecd8929b..abbcd50ff6779 100644
--- a/src/render/direct3d11/SDL_render_d3d11.c
+++ b/src/render/direct3d11/SDL_render_d3d11.c
@@ -2681,9 +2681,9 @@ static bool D3D11_RunCommandQueue(SDL_Renderer *renderer, SDL_RenderCommand *cmd
color.b *= cmd->data.color.color_scale;
if (renderer->current_colorspace == SDL_COLORSPACE_HDR10) {
- color.r = SDL_PQfromNits(color.r * 80.0f);
- color.g = SDL_PQfromNits(color.g * 80.0f);
- color.b = SDL_PQfromNits(color.b * 80.0f);
+ color.r = SDL_PQfromNits(color.r * SCRGB_NITS);
+ color.g = SDL_PQfromNits(color.g * SCRGB_NITS);
+ color.b = SDL_PQfromNits(color.b * SCRGB_NITS);
}
ID3D11DeviceContext_ClearRenderTargetView(rendererData->d3dContext, D3D11_GetCurrentRenderTargetView(renderer), &color.r);
diff --git a/src/render/direct3d12/SDL_render_d3d12.c b/src/render/direct3d12/SDL_render_d3d12.c
index 418b429fd6260..bb2f5c59be67f 100644
--- a/src/render/direct3d12/SDL_render_d3d12.c
+++ b/src/render/direct3d12/SDL_render_d3d12.c
@@ -3174,9 +3174,9 @@ static bool D3D12_RunCommandQueue(SDL_Renderer *renderer, SDL_RenderCommand *cmd
color.b *= cmd->data.color.color_scale;
if (renderer->current_colorspace == SDL_COLORSPACE_HDR10) {
- color.r = SDL_PQfromNits(color.r * 80.0f);
- color.g = SDL_PQfromNits(color.g * 80.0f);
- color.b = SDL_PQfromNits(color.b * 80.0f);
+ color.r = SDL_PQfromNits(color.r * SCRGB_NITS);
+ color.g = SDL_PQfromNits(color.g * SCRGB_NITS);
+ color.b = SDL_PQfromNits(color.b * SCRGB_NITS);
}
ID3D12GraphicsCommandList2_ClearRenderTargetView(rendererData->commandList, rtvDescriptor, &color.r, 0, NULL);
diff --git a/src/render/vulkan/SDL_render_vulkan.c b/src/render/vulkan/SDL_render_vulkan.c
index a0c26f5b3f81a..01e0d33727100 100644
--- a/src/render/vulkan/SDL_render_vulkan.c
+++ b/src/render/vulkan/SDL_render_vulkan.c
@@ -4166,9 +4166,9 @@ static bool VULKAN_RunCommandQueue(SDL_Renderer *renderer, SDL_RenderCommand *cm
color.b *= cmd->data.color.color_scale;
if (renderer->current_colorspace == SDL_COLORSPACE_HDR10) {
- color.r = SDL_PQfromNits(color.r * 80.0f);
- color.g = SDL_PQfromNits(color.g * 80.0f);
- color.b = SDL_PQfromNits(color.b * 80.0f);
+ color.r = SDL_PQfromNits(color.r * SCRGB_NITS);
+ color.g = SDL_PQfromNits(color.g * SCRGB_NITS);
+ color.b = SDL_PQfromNits(color.b * SCRGB_NITS);
}
VkClearColorValue clearColor;
diff --git a/src/video/SDL_pixels_c.h b/src/video/SDL_pixels_c.h
index ef88d42905ce5..299718741682e 100644
--- a/src/video/SDL_pixels_c.h
+++ b/src/video/SDL_pixels_c.h
@@ -27,6 +27,8 @@
#include "SDL_blit.h"
+// The value, in nits, of scRGB 1.0
+#define SCRGB_NITS 80.0f
// Pixel format functions
extern void SDL_Get8888AlphaMaskAndShift(const SDL_PixelFormatDetails *fmt, Uint32 *mask, Uint32 *shift);
diff --git a/src/video/windows/SDL_windowsmodes.c b/src/video/windows/SDL_windowsmodes.c
index ca076356cfffd..afb85e16902e7 100644
--- a/src/video/windows/SDL_windowsmodes.c
+++ b/src/video/windows/SDL_windowsmodes.c
@@ -24,6 +24,7 @@
#include "SDL_windowsvideo.h"
#include "../../events/SDL_displayevents_c.h"
+#include "../SDL_pixels_c.h"
#ifdef HAVE_DXGI1_6_H
#define COBJMACROS
@@ -546,7 +547,7 @@ static void WIN_GetHDRProperties(SDL_VideoDevice *_this, HMONITOR hMonitor, SDL_
if (WIN_GetMonitorDESC1(hMonitor, &desc)) {
if (desc.ColorSpace == DXGI_COLOR_SPACE_RGB_FULL_G2084_NONE_P2020) {
HDR->SDR_white_level = WIN_GetSDRWhitePoint(_this, hMonitor);
- HDR->HDR_headroom = (desc.MaxLuminance / 80.0f) / HDR->SDR_white_level;
+ HDR->HDR_headroom = (desc.MaxLuminance / SCRGB_NITS) / HDR->SDR_white_level;
}
}
}
diff --git a/test/testcolorspace.c b/test/testcolorspace.c
index 5b3fb54fcbcba..7f02263725ab6 100644
--- a/test/testcolorspace.c
+++ b/test/testcolorspace.c
@@ -15,6 +15,9 @@
#include <SDL3/SDL_test.h>
#include <SDL3/SDL_main.h>
+// The value, in nits, of scRGB 1.0
+#define SCRGB_NITS 80.0f
+
#define WINDOW_WIDTH 640
#define WINDOW_HEIGHT 480
@@ -85,7 +88,7 @@ static void UpdateHDRState(void)
}
SDR_white_level = SDL_GetFloatProperty(props, SDL_PROP_RENDERER_SDR_WHITE_POINT_FLOAT, 1.0f);
HDR_headroom = SDL_GetFloatProperty(props, SDL_PROP_RENDERER_HDR_HEADROOM_FLOAT, 1.0f);
- if (((SDR_white_level * 80.0f) * HDR_headroom) == 10000.0f) {
+ if (((SDR_white_level * SCRGB_NITS) * HDR_headroom) == 10000.0f) {
// The system is advertising the PQ luminance range (10000 nits)
// and tone mapping into the actual display capabilities.
// Let's use a more reasonable range for the gradient test.
@@ -693,7 +696,7 @@ static SDL_Texture *CreateHDR10Texture(int width, float max_nits)
// The white point for HDR10 textures is the SDR white level in nits
if (SDR_white_level > 1.0f) {
// We'll match the current display SDR white level so we don't get any scaling here
- SDL_SetFloatProperty(props, SDL_PROP_TEXTURE_CREATE_SDR_WHITE_POINT_FLOAT, SDR_white_level * 80.0f);
+ SDL_SetFloatProperty(props, SDL_PROP_TEXTURE_CREATE_SDR_WHITE_POINT_FLOAT, SDR_white_level * SCRGB_NITS);
} else {
// ITU-R BT.2408-6 recommends using an SDR white point of 203 nits.
SDL_SetFloatProperty(props, SDL_PROP_TEXTURE_CREATE_SDR_WHITE_POINT_FLOAT, 203.0f);