palette_update_quest_palette: tone map 1 color (#8027)

Co-authored-by: Stephen C. Wills <swills@gridprotectionalliance.org>

Source/DiabloUI/diabloui.cpp

@@ -653,7 +653,7 @@ Sint16 GetCenterOffset(Sint16 w, Sint16 bw)
 void UiLoadDefaultPalette()
 {
 	LoadPalette("ui_art\\diablo.pal", /*blend=*/false);
-	ApplyToneMapping(logical_palette, orig_palette, 256);
+	ApplyToneMapping(logical_palette, orig_palette);
 }
 
 bool UiLoadBlackBackground()
@@ -673,7 +673,7 @@ void LoadBackgroundArt(const char *pszFile, int frames)
 		return;
 
 	LoadPalInMem(pPal);
-	ApplyToneMapping(logical_palette, orig_palette, 256);
+	ApplyToneMapping(logical_palette, orig_palette);
 	UiOnBackgroundChange();
 }
 

Source/engine/palette.cpp

@@ -5,7 +5,10 @@
  */
 #include "engine/palette.h"
 
+#include <algorithm>
+#include <array>
 #include <cstdint>
+#include <span>
 
 #include <fmt/core.h>
 
@@ -79,48 +82,50 @@ void CycleColorsReverse(int from, int to)
 #endif
 }
 
-} // namespace
+// When brightness==0, then a==0 (identity mapping)
+// When brightness==100, then a==-MaxAdjustment (maximum brightening)
+constexpr float CalculateToneMappingParameter(int brightness)
+{
+	// Maximum adjustment factor (tweak this constant to change the effect strength)
+	constexpr float MaxAdjustment = 2.0F;
+	return -(brightness / 100.0f) * MaxAdjustment;
+}
 
-void palette_update(int first, int ncolor)
+constexpr uint8_t MapTone(float a, uint8_t color)
 {
-	if (HeadlessMode)
-		return;
+	const auto x = static_cast<float>(color / 255.0f);
+	// Our quadratic tone mapping: f(x) = a*x^2 + (1-a)*x.
+	const float y = std::clamp(a * x * x + (1.0f - a) * x, 0.0f, 1.0f);
+	return static_cast<uint8_t>(y * 255.0f + 0.5f);
+}
 
-	assert(Palette);
-	if (SDLC_SetSurfaceAndPaletteColors(PalSurface, Palette.get(), system_palette.data(), first, ncolor) < 0) {
-		ErrSdl();
-	}
-	pal_surface_palette_version++;
+void ApplyToneMappingSingleColor(SDL_Color &dst, const SDL_Color &src)
+{
+	const float a = CalculateToneMappingParameter(*GetOptions().Graphics.brightness);
+	dst.r = MapTone(a, src.r);
+	dst.g = MapTone(a, src.g);
+	dst.b = MapTone(a, src.b);
 }
 
+} // namespace
+
 // Applies a tone mapping curve based on the brightness slider value.
 // The brightness value is in the range [0, 100] where 0 is neutral (no change)
 // and 100 produces maximum brightening.
-void ApplyToneMapping(std::array<SDL_Color, 256> &dst,
-    const std::array<SDL_Color, 256> &src,
-    int n)
+void ApplyToneMapping(std::array<SDL_Color, 256> &dst, std::span<const SDL_Color, 256> src)
 {
 	// Get the brightness slider value (0 = neutral, 100 = max brightening)
-	int brightnessSlider = *GetOptions().Graphics.brightness; // New brightness setting.
-
-	// Maximum adjustment factor (tweak this constant to change the effect strength)
-	const float maxAdjustment = 2.0f;
-	// Compute the quadratic parameter:
-	// When brightnessSlider==0, then a==0 (identity mapping)
-	// When brightnessSlider==100, then a== -maxAdjustment (maximum brightening)
-	float a = -(brightnessSlider / 100.0f) * maxAdjustment;
+	const int brightnessSlider = *GetOptions().Graphics.brightness;
 
 	// Precompute a lookup table for speed.
+	const float a = CalculateToneMappingParameter(brightnessSlider);
 	uint8_t toneMap[256];
 	for (int i = 0; i < 256; i++) {
-		float x = i / 255.0f;
-		// Our quadratic tone mapping: f(x) = a*x^2 + (1-a)*x.
-		const float y = std::clamp(a * x * x + (1.0f - a) * x, 0.0f, 1.0f);
-		toneMap[i] = static_cast<uint8_t>(y * 255.0f + 0.5f);
+		toneMap[i] = MapTone(a, i);
 	}
 
 	// Apply the lookup table to each color channel in the palette.
-	for (int i = 0; i < n; i++) {
+	for (int i = 0; i < 256; i++) {
 		dst[i].r = toneMap[src[i].r];
 		dst[i].g = toneMap[src[i].g];
 		dst[i].b = toneMap[src[i].b];
@@ -128,6 +133,18 @@ void ApplyToneMapping(std::array<SDL_Color, 256> &dst,
 	RedrawEverything();
 }
 
+void palette_update(int first, int ncolor)
+{
+	if (HeadlessMode)
+		return;
+
+	assert(Palette);
+	if (SDLC_SetSurfaceAndPaletteColors(PalSurface, Palette.get(), system_palette.data(), first, ncolor) < 0) {
+		ErrSdl();
+	}
+	pal_surface_palette_version++;
+}
+
 void palette_init()
 {
 	LoadBrightness();
@@ -206,7 +223,7 @@ void IncreaseBrightness()
 	if (brightnessValue < 100) {
 		int newBrightness = std::min(brightnessValue + 5, 100);
 		GetOptions().Graphics.brightness.SetValue(newBrightness);
-		ApplyToneMapping(system_palette, logical_palette, 256);
+		ApplyToneMapping(system_palette, logical_palette);
 		palette_update();
 	}
 }
@@ -217,7 +234,7 @@ void DecreaseBrightness()
 	if (brightnessValue > 0) {
 		int newBrightness = std::max(brightnessValue - 5, 0);
 		GetOptions().Graphics.brightness.SetValue(newBrightness);
-		ApplyToneMapping(system_palette, logical_palette, 256);
+		ApplyToneMapping(system_palette, logical_palette);
 		palette_update();
 	}
 }
@@ -226,7 +243,7 @@ int UpdateBrightness(int brightness)
 {
 	if (brightness >= 0) {
 		GetOptions().Graphics.brightness.SetValue(brightness);
-		ApplyToneMapping(system_palette, logical_palette, 256);
+		ApplyToneMapping(system_palette, logical_palette);
 		palette_update();
 	}
 
@@ -267,7 +284,7 @@ void PaletteFadeIn(int fr, const std::array<SDL_Color, 256> &srcPalette)
 	if (demo::IsRunning())
 		fr = 0;
 
-	ApplyToneMapping(logical_palette, srcPalette, 256);
+	ApplyToneMapping(logical_palette, srcPalette);
 
 	if (fr > 0) {
 		const uint32_t tc = SDL_GetTicks();
@@ -368,10 +385,11 @@ void palette_update_hive()
 
 void palette_update_quest_palette(int n)
 {
-	int i = 32 - n;
+	// n is in [1, 32], so `i` is in [0, 31].
+	const int i = 32 - n;
 	logical_palette[i] = orig_palette[i];
-	ApplyToneMapping(system_palette, logical_palette, 32);
-	palette_update(0, 31);
+	ApplyToneMappingSingleColor(system_palette[i], logical_palette[i]);
+	palette_update(i, 1);
 	UpdateBlendedLookupTableSingleColor(i, logical_palette.data(), /*skipFrom=*/1, /*skipTo=*/31);
 }
 

Source/engine/palette.h

@@ -7,6 +7,7 @@
 
 #include <array>
 #include <cstdint>
+#include <span>
 
 #include <SDL.h>
 
@@ -43,7 +44,7 @@ void palette_init();
 void LoadPalette(const char *pszFileName, bool blend = true);
 void LoadRndLvlPal(dungeon_type l);
 void IncreaseBrightness();
-void ApplyToneMapping(std::array<SDL_Color, 256> &dst, const std::array<SDL_Color, 256> &src, int n);
+void ApplyToneMapping(std::array<SDL_Color, 256> &dst, std::span<const SDL_Color, 256> src);
 void DecreaseBrightness();
 int UpdateBrightness(int sliderValue);
 void BlackPalette();

Source/interfac.cpp

@@ -479,7 +479,7 @@ void ProgressEventHandler(const SDL_Event &event, uint16_t modState)
 				if (RenderDirectlyToOutputSurface && PalSurface != nullptr) {
 					// The loading thread sets `orig_palette`, so we make sure to use
 					// our own palette for drawing the foreground.
-					ApplyToneMapping(logical_palette, ProgressEventHandlerState.palette, 256);
+					ApplyToneMapping(logical_palette, ProgressEventHandlerState.palette);
 
 					// Ensure that all back buffers have the full progress bar.
 					const void *initialPixels = PalSurface->pixels;