Move the blend_rgb() method to sdl/utils and rename it to blend_rgba.

Added support for an alpha value.

src/attack_prediction_display.cpp

@@ -505,16 +505,16 @@ void battle_prediction_pane::get_hp_distrib_surface(const std::vector<std::pair<
 		int bar_len = std::max<int>(static_cast<int>((prob * (bar_space - 4)) + 0.5), 2);
 
 		SDL_Rect bar_rect_1 = sdl::create_rect(hp_sep + 4, 6 + (fs + 2) * i, bar_len, 8);
-		sdl::fill_rect(surf, &bar_rect_1, blend_rgb(surf, row_color.r, row_color.g, row_color.b, 100));
+		sdl::fill_rect(surf, &bar_rect_1, blend_rgba(surf, row_color.r, row_color.g, row_color.b, row_color.unused, 100));
 
 		SDL_Rect bar_rect_2 = sdl::create_rect(hp_sep + 4, 7 + (fs + 2) * i, bar_len, 6);
-		sdl::fill_rect(surf, &bar_rect_2, blend_rgb(surf, row_color.r, row_color.g, row_color.b, 66));
+		sdl::fill_rect(surf, &bar_rect_2, blend_rgba(surf, row_color.r, row_color.g, row_color.b, row_color.unused, 66));
 
 		SDL_Rect bar_rect_3 = sdl::create_rect(hp_sep + 4, 8 + (fs + 2) * i, bar_len, 4);
-		sdl::fill_rect(surf, &bar_rect_3, blend_rgb(surf, row_color.r, row_color.g, row_color.b, 33));
+		sdl::fill_rect(surf, &bar_rect_3, blend_rgba(surf, row_color.r, row_color.g, row_color.b, row_color.unused, 33));
 
 		SDL_Rect bar_rect_4 = sdl::create_rect(hp_sep + 4, 9 + (fs + 2) * i, bar_len, 2);
-		sdl::fill_rect(surf, &bar_rect_4, blend_rgb(surf, row_color.r, row_color.g, row_color.b, 0));
+		sdl::fill_rect(surf, &bar_rect_4, blend_rgba(surf, row_color.r, row_color.g, row_color.b, row_color.unused, 0));
 
 		// Draw probability percentage, aligned right.
 		format_prob(str_buf, prob);
@@ -524,16 +524,6 @@ void battle_prediction_pane::get_hp_distrib_surface(const std::vector<std::pair<
 	}
 }
 
-Uint32 battle_prediction_pane::blend_rgb(const surface& surf, unsigned char r, unsigned char g, unsigned char b, unsigned char drop)
-{
-	// We simply decrement each component.
-	if(r < drop) r = 0; else r -= drop;
-	if(g < drop) g = 0; else g -= drop;
-	if(b < drop) b = 0; else b -= drop;
-
-	return SDL_MapRGB(surf->format, r, g, b);
-}
-
 attack_prediction_displayer::RESULT attack_prediction_displayer::button_pressed(int selection)
 {
 	// Get the selected weapon, if any.

src/attack_prediction_display.hpp

@@ -107,13 +107,6 @@ class battle_prediction_pane : public gui::preview_pane
 							const battle_context_unit_stats& stats,
 								const battle_context_unit_stats& opp_stats,
 								surface& surf, int& width, int& height);
-
-	// This method blends a RGB color. The method takes as input a surface,
-	// the RGB color to blend and a value specifying how much blending to
-	// apply. The blended color is returned. Caution: if you use a
-	// transparent color, make sure the resulting color is not equal to the
-	// transparent color.
-	Uint32 blend_rgb(const surface& surf, unsigned char r, unsigned char g, unsigned char b, unsigned char drop);
 };
 
 // This class is used when the user clicks on the button

src/sdl/utils.cpp

@@ -374,6 +374,16 @@ scale_surface_down(surface& dst, const surface& src, const int w_dst, const int
 
 #endif
 
+Uint32 blend_rgba(const surface& surf, unsigned char r, unsigned char g, unsigned char b, unsigned char a, unsigned char drop)
+{
+	// We simply decrement each component.
+	if(r < drop) r = 0; else r -= drop;
+	if(g < drop) g = 0; else g -= drop;
+	if(b < drop) b = 0; else b -= drop;
+
+	return SDL_MapRGBA(surf->format, r, g, b, a);
+}
+
 surface scale_surface_xbrz(const surface & surf, size_t z)
 {
 	if(surf == NULL)

src/sdl/utils.hpp

@@ -113,6 +113,16 @@ inline void sdl_blit(const surface& src, SDL_Rect* src_rect, surface& dst, SDL_R
 	SDL_BlitSurface(src, src_rect, dst, dst_rect);
 }
 
+/**
+ * This method blends a RGBA color. The method takes as input a surface,
+ * the RGB color to blend and a value specifying how much blending to apply.
+ * The blended color is returned.
+ * Caution: if you use a transparent color,
+ * make sure the resulting color is not equal to the transparent color.
+ */
+Uint32 blend_rgba(const surface& surf, unsigned char r, unsigned char g, unsigned char b,
+		unsigned char a, unsigned char drop);
+
 /**
  * Check that the surface is neutral bpp 32.
  *