Dye: Cast to SDL_Color rather than shifting bits around

When we use SDL_PIXELFORMAT_RGBA32, which is actually the same as
SDL_PIXELFORMAT_ABGR8888 on little-endian systems, we can cast the pixel
data directly to SDL_Color* for easy access to the components.

This may also make applying dye more efficient on big-endian systems,
though I have no such system to test with.

Follow-up to d8b871727c363892b14f2eadfad8f6058ec6ab72.

3 files changed, 35 insertions, 32 deletions

diff --git a/src/resources/dye.cpp b/src/resources/dye.cpp
index d594299c..0ecc9fd6 100644
--- a/src/resources/dye.cpp
+++ b/src/resources/dye.cpp
@@ -70,7 +70,7 @@ DyePalette::DyePalette(const std::string &description)
 
             v = (v << 4) | n;
         }
-        Color c = { { (unsigned char) (v >> 16), (unsigned char) (v >> 8), (unsigned char) v } };
+        Color c = { (unsigned char) (v >> 16), (unsigned char) (v >> 8), (unsigned char) v };
         mColors.push_back(c);
         pos += 6;
 
@@ -103,9 +103,9 @@ void DyePalette::getColor(int intensity, int color[3]) const
 
     int j = t != 0 ? i : i - 1;
     // Get the exact color if any, the next color otherwise.
-    int r2 = mColors[j].value[0],
-        g2 = mColors[j].value[1],
-        b2 = mColors[j].value[2];
+    int r2 = mColors[j].r,
+        g2 = mColors[j].g,
+        b2 = mColors[j].b;
 
     if (t == 0)
     {
@@ -120,9 +120,9 @@ void DyePalette::getColor(int intensity, int color[3]) const
     int r1 = 0, g1 = 0, b1 = 0;
     if (i > 0)
     {
-        r1 = mColors[i - 1].value[0];
-        g1 = mColors[i - 1].value[1];
-        b1 = mColors[i - 1].value[2];
+        r1 = mColors[i - 1].r;
+        g1 = mColors[i - 1].g;
+        b1 = mColors[i - 1].b;
     }
 
     // Perform a linear interpolation.
@@ -153,9 +153,9 @@ void DyePalette::getColor(double intensity, int color[3]) const
     if (i == j)
     {
         // Exact color.
-        color[0] = mColors[i].value[0];
-        color[1] = mColors[i].value[1];
-        color[2] = mColors[i].value[2];
+        color[0] = mColors[i].r;
+        color[1] = mColors[i].g;
+        color[2] = mColors[i].b;
         return;
     }
 
@@ -163,12 +163,12 @@ void DyePalette::getColor(double intensity, int color[3]) const
     double rest = 1 - intensity;
 
     // Get the colors
-    int r1 = mColors[i].value[0],
-        g1 = mColors[i].value[1],
-        b1 = mColors[i].value[2],
-        r2 = mColors[j].value[0],
-        g2 = mColors[j].value[1],
-        b2 = mColors[j].value[2];
+    int r1 = mColors[i].r,
+        g1 = mColors[i].g,
+        b1 = mColors[i].b,
+        r2 = mColors[j].r,
+        g2 = mColors[j].g,
+        b2 = mColors[j].b;
 
     // Perform the interpolation.
     color[0] = (rest * r1 + intensity * r2);
diff --git a/src/resources/dye.h b/src/resources/dye.h
index 61ad4df2..0fe68f07 100644
--- a/src/resources/dye.h
+++ b/src/resources/dye.h
@@ -30,7 +30,6 @@
 class DyePalette
 {
     public:
-
         /**
          * Creates a palette based on the given string.
          * The string is either a file name or a sequence of hexadecimal RGB
@@ -50,8 +49,12 @@ class DyePalette
         void getColor(double intensity, int color[3]) const;
 
     private:
-
-        struct Color { unsigned char value[3]; };
+        struct Color
+        {
+            unsigned char r;
+            unsigned char g;
+            unsigned char b;
+        };
 
         std::vector<Color> mColors;
 };
@@ -62,7 +65,6 @@ class DyePalette
 class Dye
 {
     public:
-
         /**
          * Creates a set of palettes based on the given string.
          *
diff --git a/src/resources/image.cpp b/src/resources/image.cpp
index 158d5956..b36aea01 100644
--- a/src/resources/image.cpp
+++ b/src/resources/image.cpp
@@ -121,12 +121,12 @@ Resource *Image::load(SDL_RWops *rw, const Dye &dye)
         return nullptr;
     }
 
-    if (surf->format->format != SDL_PIXELFORMAT_ABGR8888)
+    if (surf->format->format != SDL_PIXELFORMAT_RGBA32)
     {
-        logger->log("Warning: image format is %s, not SDL_PIXELFORMAT_ABGR8888. Converting...",
+        logger->log("Warning: image format is %s, not SDL_PIXELFORMAT_RGBA32. Converting...",
                     SDL_GetPixelFormatName(surf->format->format));
 
-        SDL_Surface *convertedSurf = SDL_ConvertSurfaceFormat(surf, SDL_PIXELFORMAT_ABGR8888, 0);
+        SDL_Surface *convertedSurf = SDL_ConvertSurfaceFormat(surf, SDL_PIXELFORMAT_RGBA32, 0);
         SDL_FreeSurface(surf);
         if (!convertedSurf)
         {
@@ -136,17 +136,18 @@ Resource *Image::load(SDL_RWops *rw, const Dye &dye)
         surf = convertedSurf;
     }
 
-    auto *pixels = static_cast< uint32_t * >(surf->pixels);
-    for (uint32_t *p_end = pixels + surf->w * surf->h; pixels != p_end; ++pixels)
+    auto *pixels = static_cast<SDL_Color *>(surf->pixels);
+    for (SDL_Color *p_end = pixels + surf->w * surf->h; pixels != p_end; ++pixels)
     {
-        const uint32_t alpha = (*pixels >> 24) & 255;
-        if (!alpha) continue;
-        int v[3];
-        v[0] = (*pixels) & 255;
-        v[1] = (*pixels >> 8) & 255;
-        v[2] = (*pixels >> 16) & 255;
+        if (!pixels->a)
+            continue;
+
+        int v[3] = { pixels->r, pixels->g, pixels->b };
         dye.update(v);
-        *pixels = (alpha << 24) | (v[2] << 16) | (v[1] << 8) | v[0];
+
+        pixels->r = v[0];
+        pixels->g = v[1];
+        pixels->b = v[2];
     }
 
     Image *image = load(surf);