From 8b17e2ef62bd1528c42e89e5d60bb9ba9ec350ee Mon Sep 17 00:00:00 2001
From: Maarten ter Huurne <maarten@treewalker.org>
Date: Thu, 2 Jun 2011 06:19:21 +0200
Subject: [PATCH] PNG: Make loadPNG() responsible for creating an RGBA surface.

Before this commit loadPNG() could return any surface format and the caller
was responsible for converting it to the desired format. However, in practice
all callers want a surface with an alpha channel and SDL only supports that
with 32bpp surfaces, so RGBA or a permutation thereof. So I changed the
contract for loadPNG() so it is required to return an RGBA surface, and
removed the conversion code in the callers.

The next step is to replace IMG_Load() by a function that calls libpng
directly and loads a fixed 32bpp pixel format. That way, we can drop the
SDL_image dependency and avoid unnecessary pixel format conversions.
---
 src/asfont.cpp  | 29 ++---------------------------
 src/imageio.cpp | 34 +++++++++++++++++++++++++++++++---
 src/imageio.h   |  2 ++
 src/surface.cpp |  7 ++-----
 4 files changed, 37 insertions(+), 35 deletions(-)

diff --git a/src/asfont.cpp b/src/asfont.cpp
index c74015d..401bd12 100644
--- a/src/asfont.cpp
+++ b/src/asfont.cpp
@@ -11,35 +11,10 @@
 ASFont::ASFont(const std::string &fontImagePath)
 	: characters(SFONTPLUS_CHARSET)
 {
-	// Load PNG file into an SDL surface.
-	SDL_Surface *buf = loadPNG(fontImagePath);
-	if (!buf) {
-		surface = NULL;
+	surface = loadPNG(fontImagePath);
+	if (!surface) {
 		return;
 	}
-
-	// Make sure we have a surface that can be blitted using alpha blending.
-	if (buf->format->BytesPerPixel == 4) {
-		surface = buf;
-		SDL_SetAlpha(surface, SDL_SRCALPHA, 255);
-	} else {
-		SDL_PixelFormat format32;
-		memset(&format32, 0, sizeof(format32));
-		format32.BitsPerPixel = 32;
-		format32.BytesPerPixel = 4;
-		format32.Rmask =
-			SDL_BYTEORDER == SDL_BIG_ENDIAN ? 0x00FF0000 : 0x000000FF;
-		format32.Gmask = 0x0000FF00;
-		format32.Bmask =
-			SDL_BYTEORDER == SDL_BIG_ENDIAN ? 0x000000FF : 0x00FF0000;
-		format32.Amask = 0xFF000000;
-		format32.Rshift = SDL_BYTEORDER == SDL_BIG_ENDIAN ? 16 : 0;
-		format32.Gshift = 8;
-		format32.Bshift = SDL_BYTEORDER == SDL_BIG_ENDIAN ? 0 : 16;
-		format32.Ashift = 24;
-		surface = SDL_ConvertSurface(buf, &format32, SDL_SRCALPHA);
-		SDL_FreeSurface(buf);
-	}
 	assert(surface->format->BytesPerPixel == 4);
 
 	SDL_LockSurface(surface);
diff --git a/src/imageio.cpp b/src/imageio.cpp
index aeebbcb..b9b8921 100644
--- a/src/imageio.cpp
+++ b/src/imageio.cpp
@@ -2,7 +2,35 @@
 
 #include <SDL_image.h>
 
-SDL_Surface *loadPNG(const std::string &path)
-{
-	return IMG_Load(path.c_str());
+SDL_Surface *loadPNG(const std::string &path) {
+	// Load PNG file into an SDL surface.
+	SDL_Surface *surface = IMG_Load(path.c_str());
+	if (!surface) {
+		return NULL;
+	}
+
+	// Make sure we have a surface that can be blitted using alpha blending.
+	if (surface->format->BytesPerPixel == 4) {
+		SDL_SetAlpha(surface, SDL_SRCALPHA, 255);
+		return surface;
+	} else {
+		SDL_PixelFormat format32;
+		memset(&format32, 0, sizeof(format32));
+		format32.BitsPerPixel = 32;
+		format32.BytesPerPixel = 4;
+		format32.Rmask =
+			SDL_BYTEORDER == SDL_BIG_ENDIAN ? 0x00FF0000 : 0x000000FF;
+		format32.Gmask = 0x0000FF00;
+		format32.Bmask =
+			SDL_BYTEORDER == SDL_BIG_ENDIAN ? 0x000000FF : 0x00FF0000;
+		format32.Amask = 0xFF000000;
+		format32.Rshift = SDL_BYTEORDER == SDL_BIG_ENDIAN ? 16 : 0;
+		format32.Gshift = 8;
+		format32.Bshift = SDL_BYTEORDER == SDL_BIG_ENDIAN ? 0 : 16;
+		format32.Ashift = 24;
+		SDL_Surface *surface32 =
+			SDL_ConvertSurface(surface, &format32, SDL_SRCALPHA);
+		SDL_FreeSurface(surface);
+		return surface32;
+	}
 }
diff --git a/src/imageio.h b/src/imageio.h
index 3e4e48f..54d4640 100644
--- a/src/imageio.h
+++ b/src/imageio.h
@@ -5,6 +5,8 @@
 
 struct SDL_Surface;
 
+/** Loads an image from a PNG file into a newly allocated 32bpp RGBA surface.
+  */
 SDL_Surface *loadPNG(const std::string &path);
 
 #endif
diff --git a/src/surface.cpp b/src/surface.cpp
index 264ea3c..20808b8 100644
--- a/src/surface.cpp
+++ b/src/surface.cpp
@@ -90,11 +90,8 @@ void Surface::load(const string &img, const string &skin) {
 		skinpath = img;
 	}
 
-	SDL_Surface *buf = loadPNG(skinpath);
-	if (buf!=NULL) {
-		raw = SDL_DisplayFormatAlpha(buf);
-		SDL_FreeSurface(buf);
-	} else {
+	raw = loadPNG(skinpath);
+	if (!raw) {
 		ERROR("Couldn't load surface '%s'\n", img.c_str());
 	}
 }