Fix SDL color encoding.

Little-endian + RGBA means that red is located at the lowest-order bits,
not the highest.

The hello_world_sdl test is now portable, because we no longer write to
individual bytes.

We also add a test for a completely blank screen, which should be black, not
red.

Closes #1287, #761, #765.

5 files changed, 34 insertions, 20 deletions

diff --git a/src/library_sdl.js b/src/library_sdl.js
index 5aaddb3b..356c9746 100644
--- a/src/library_sdl.js
+++ b/src/library_sdl.js
@@ -242,7 +242,7 @@ var LibrarySDL = {
     },
 
     translateColorToCSSRGBA: function(rgba) {
-      return 'rgba(' + ((rgba >> 24)&255) + ',' + ((rgba >> 16)&255) + ',' + ((rgba >> 8)&255) + ',' + ((rgba&255)/255) + ')';
+      return 'rgba(' + (rgba&0xff) + ',' + (rgba>>8 & 0xff) + ',' + (rgba>>16 & 0xff) + ',' + (rgba>>>24)/0xff + ')';
     },
 
     translateRGBAToCSSRGBA: function(r, g, b, a) {
@@ -250,7 +250,7 @@ var LibrarySDL = {
     },
 
     translateRGBAToColor: function(r, g, b, a) {
-      return (r << 24) + (g << 16) + (b << 8) + a;
+      return r | g << 8 | b << 16 | a << 24;
     },
 
     makeSurface: function(width, height, flags, usePageCanvas, source, rmask, gmask, bmask, amask) {
@@ -819,7 +819,6 @@ var LibrarySDL = {
     if (surfData.isFlagSet(0x00200000 /* SDL_HWPALETTE */)) {
       SDL.copyIndexedColorData(surfData);
     } else if (!surfData.colors) {
-      var num = surfData.image.data.length;
       var data = surfData.image.data;
       var buffer = surfData.buffer;
 #if USE_TYPED_ARRAYS == 2
@@ -827,17 +826,14 @@ var LibrarySDL = {
       var src = buffer >> 2;
       var dst = 0;
       var isScreen = surf == SDL.screen;
+      var data32 = new Uint32Array(data.buffer);
+      var num = data32.length;
       while (dst < num) {
-        // TODO: access underlying data buffer and write in 32-bit chunks or more
-        var val = HEAP32[src]; // This is optimized. Instead, we could do {{{ makeGetValue('buffer', 'dst', 'i32') }}};
-        data[dst  ] = val & 0xff;
-        data[dst+1] = (val >> 8) & 0xff;
-        data[dst+2] = (val >> 16) & 0xff;
-        data[dst+3] = isScreen ? 0xff : ((val >> 24) & 0xff);
-        src++;
-        dst += 4;
+        // HEAP32[src++] is an optimization. Instead, we could do {{{ makeGetValue('buffer', 'dst', 'i32') }}};
+        data32[dst++] = HEAP32[src++] | (isScreen ? 0xff000000 : 0);
       }
 #else
+      var num = surfData.image.data.length;
       for (var i = 0; i < num; i++) {
         // We may need to correct signs here. Potentially you can hardcode a write of 255 to alpha, say, and
         // the compiler may decide to write -1 in the llvm bitcode...
@@ -1120,13 +1116,13 @@ var LibrarySDL = {
   },
 
   SDL_MapRGB: function(fmt, r, g, b) {
-    // Canvas screens are always RGBA
-    return 0xff+((b&0xff)<<8)+((g&0xff)<<16)+((r&0xff)<<24)
+    // Canvas screens are always RGBA. We assume the machine is little-endian.
+    return r&0xff|(g&0xff)<<8|(b&0xff)<<16|0xff000000;
   },
 
   SDL_MapRGBA: function(fmt, r, g, b, a) {
-    // Canvas screens are always RGBA
-    return (a&0xff)+((b&0xff)<<8)+((g&0xff)<<16)+((r&0xff)<<24)
+    // Canvas screens are always RGBA. We assume the machine is little-endian.
+    return r&0xff|(g&0xff)<<8|(b&0xff)<<16|(a&0xff)<<24;
   },
 
   SDL_GetAppState: function() {
diff --git a/tests/hello_world_sdl.cpp b/tests/hello_world_sdl.cpp
index b6401995..eeaad0cd 100644
--- a/tests/hello_world_sdl.cpp
+++ b/tests/hello_world_sdl.cpp
@@ -2,7 +2,7 @@
 #include <SDL/SDL.h>
 
 
-int main() {
+extern "C" int main(int argc, char** argv) {
   printf("hello, world!\n");
 
   SDL_Init(SDL_INIT_VIDEO);
@@ -11,10 +11,8 @@ int main() {
   if (SDL_MUSTLOCK(screen)) SDL_LockSurface(screen);
   for (int i = 0; i < 256; i++) {
     for (int j = 0; j < 256; j++) {
-      *((char*)screen->pixels + i*256*4 + j*4 + 0) = i;
-      *((char*)screen->pixels + i*256*4 + j*4 + 1) = j;
-      *((char*)screen->pixels + i*256*4 + j*4 + 2) = 255-i;
-      *((char*)screen->pixels + i*256*4 + j*4 + 3) = (i+j)%255; // actually ignored, since this is to the screen
+      // alpha component is actually ignored, since this is to the screen
+      *((Uint32*)screen->pixels + i * 256 + j) = SDL_MapRGBA(screen->format, i, j, 255-i, (i+j) % 255);
     }
   }
   if (SDL_MUSTLOCK(screen)) SDL_UnlockSurface(screen);
diff --git a/tests/runner.py b/tests/runner.py
index e7434479..4b8a3010 100755
--- a/tests/runner.py
+++ b/tests/runner.py
@@ -12735,6 +12735,9 @@ elif 'browser' in str(sys.argv):
     def test_cube_explosion(self):
       self.btest('cube_explosion.c', expected=['667220544', '-1543354600', '-1485258415'])
 
+    def test_sdl_canvas_blank(self):
+      self.btest('sdl_canvas_blank.c', reference='sdl_canvas_blank.png')
+
     def test_sdl_canvas_palette(self):
       self.btest('sdl_canvas_palette.c', reference='sdl_canvas_palette.png')
 
diff --git a/tests/sdl_canvas_blank.c b/tests/sdl_canvas_blank.c
new file mode 100644
index 00000000..0e7607a6
--- /dev/null
+++ b/tests/sdl_canvas_blank.c
@@ -0,0 +1,17 @@
+#include <stdio.h>
+#include <SDL/SDL.h>
+
+
+int main() {
+  SDL_Init(SDL_INIT_VIDEO);
+  SDL_Surface *screen = SDL_SetVideoMode(256, 256, 32, SDL_SWSURFACE);
+
+  if (SDL_MUSTLOCK(screen)) SDL_LockSurface(screen);
+  if (SDL_MUSTLOCK(screen)) SDL_UnlockSurface(screen);
+  SDL_Flip(screen); 
+
+  SDL_Quit();
+
+  return 0;
+}
+
diff --git a/tests/sdl_canvas_blank.png b/tests/sdl_canvas_blank.png
new file mode 100644
index 00000000..dc5a4a26
--- /dev/null
+++ b/tests/sdl_canvas_blank.png