Optimize I_MapRGB

Replaced the `I_MapRGB()` function with a preprocessor macro to manually assemble 32-bit pixel values. This approach avoids the overhead of the `SDL_MapRGB()` function call, resulting in situational performance improvements when working with non-palettized, fixed pixel formats.

The macro handles:
- Shifting R, G, B components according to the format's `Rshift`, `Gshift`, `Bshift`.
- Adjusting for bit loss using `Rloss`, `Gloss`, `Bloss`.
- Applying the alpha mask (`Amask`) for consistency.

This change is safe under the assumption of a fixed 32-bit pixel format (e.g., ARGB8888).

src/i_video.c

@@ -88,7 +88,7 @@ static int vid_window_title_short = 1;
 #ifndef CRISPY_TRUECOLOR
 static SDL_Surface *screenbuffer = NULL;
 #endif
-static SDL_Surface *argbbuffer = NULL;
+SDL_Surface *argbbuffer = NULL;
 static SDL_Texture *texture = NULL;
 static SDL_Texture *texture_upscaled = NULL;
 
@@ -2291,9 +2291,12 @@ void I_BindVideoVariables(void)
     M_BindIntVariable("mouse_grab",                    &mouse_grab);
 }
 
+// [PN] Original human-readable mapping function from Crispy Doom
+/*
 #ifdef CRISPY_TRUECOLOR
 const pixel_t I_MapRGB (const uint8_t r, const uint8_t g, const uint8_t b)
 {
 	return SDL_MapRGB(argbbuffer->format, r, g, b);
 }
 #endif
+*/

src/i_video.h

@@ -21,6 +21,7 @@
 #ifndef __I_VIDEO__
 #define __I_VIDEO__
 
+#include "SDL.h"
 #include "doomtype.h"
 #include "i_truecolor.h"
 #include "m_fixed.h"
@@ -97,7 +98,24 @@ void I_SetPalette (byte* palette);
 int I_GetPaletteIndex(int r, int g, int b);
 #else
 void I_SetPalette (int palette);
-extern const pixel_t I_MapRGB (const uint8_t r, const uint8_t g, const uint8_t b);
+
+// [PN] We define a macro that manually assembles a 32-bit pixel from separate R/G/B values.
+// It applies the format's shift and loss adjustments, then merges all components (and alpha mask) with bitwise OR.
+// This avoids the overhead of the SDL_MapRGB() function call.
+//
+// Original human-readable mapping function from Crispy Doom is preserved as commented example in i_video.c file.
+// extern inline const pixel_t I_MapRGB (const uint8_t r, const uint8_t g, const uint8_t b);
+
+extern SDL_Surface *argbbuffer;
+
+#define I_MapRGB(r, g, b) ( \
+    (pixel_t)( \
+        (((uint32_t)(r) >> argbbuffer->format->Rloss) << argbbuffer->format->Rshift) | \
+        (((uint32_t)(g) >> argbbuffer->format->Gloss) << argbbuffer->format->Gshift) | \
+        (((uint32_t)(b) >> argbbuffer->format->Bloss) << argbbuffer->format->Bshift) | \
+        (argbbuffer->format->Amask) \
+    ) \
+)
 #endif
 void I_FinishUpdate (void);