Add BGRa for compatibility with cairo

PIL/ImageMode.py

@@ -40,6 +40,7 @@ def getmode(mode):
             _modes[m] = ModeDescriptor(m, bands, basemode, basetype)
         # extra experimental modes
         _modes["RGBa"] = ModeDescriptor("RGBa", ("R", "G", "B", "a"), "RGB", "L")
+        _modes["BGRa"] = ModeDescriptor("BGRa", ("B", "G", "R", "a"), "BGR", "L")
         _modes["LA"] = ModeDescriptor("LA", ("L", "A"), "L", "L")
         _modes["La"] = ModeDescriptor("La", ("L", "a"), "L", "L")
         _modes["PA"] = ModeDescriptor("PA", ("P", "A"), "RGB", "L")

libImaging/Convert.c

@@ -454,6 +454,21 @@ rgbA2rgba(UINT8* out, const UINT8* in, int xsize)
     }
 }
 
+static void
+rgbA2bgra(UINT8* out, const UINT8* in, int xsize)
+{
+    int x;
+    unsigned int alpha, tmp;
+    for (x = 0; x < xsize; x++) {
+        alpha = in[3];
+        *out++ = MULDIV255(in[2], alpha, tmp);
+        *out++ = MULDIV255(in[1], alpha, tmp);
+        *out++ = MULDIV255(in[0], alpha, tmp);
+        *out++ = in[3];
+        in += 4;
+    }
+}
+
 /* RGBa -> RGBA conversion to remove premultiplication
    Needed for correct transforms/resizing on RGBA images */
 static void
@@ -476,6 +491,26 @@ rgba2rgbA(UINT8* out, const UINT8* in, int xsize)
     }
 }
 
+static void
+bgra2rgbA(UINT8* out, const UINT8* in, int xsize)
+{
+    int x;
+    unsigned int alpha;
+    for (x = 0; x < xsize; x++, in+=4) {
+        alpha = in[3];
+        if (alpha == 255 || alpha == 0) {
+            *out++ = in[2];
+            *out++ = in[1];
+            *out++ = in[0];
+        } else {
+            *out++ = CLIP((255 * in[2]) / alpha);
+            *out++ = CLIP((255 * in[1]) / alpha);
+            *out++ = CLIP((255 * in[0]) / alpha);
+        }
+        *out++ = in[3];
+    }
+}
+
 /*
  * Conversion of RGB + single transparent color to RGBA,
  * where any pixel that matches the color will have the
@@ -834,11 +869,13 @@ static struct {
     { "RGBA", "F", rgb2f },
     { "RGBA", "RGB", rgba2rgb },
     { "RGBA", "RGBa", rgbA2rgba },
+    { "RGBA", "BGRa", rgbA2bgra },
     { "RGBA", "RGBX", rgb2rgba },
     { "RGBA", "CMYK", rgb2cmyk },
     { "RGBA", "YCbCr", ImagingConvertRGB2YCbCr },
 
     { "RGBa", "RGBA", rgba2rgbA },
+    { "BGRa", "RGBA", bgra2rgbA },
 
     { "RGBX", "1", rgb2bit },
     { "RGBX", "L", rgb2l },

libImaging/Pack.c

@@ -534,6 +534,7 @@ static struct {
     {"RGBa",	"RGBa",		32,	copy4},
     {"RGBa",	"BGRa",		32,	ImagingPackBGRA},
     {"RGBa",	"aBGR",		32,	ImagingPackABGR},
+    {"BGRa",	"BGRa",		32,	copy4},
 
     /* true colour w. padding */
     {"RGBX",	"RGBX",		32,	copy4},

libImaging/Storage.c

@@ -179,6 +179,11 @@ ImagingNewPrologueSubtype(const char *mode, int xsize, int ysize,
         im->bands = im->pixelsize = 4;
         im->linesize = xsize * 4;
 
+    } else if (strcmp(mode, "BGRa") == 0) {
+        /* 32-bit true colour images with premultiplied alpha */
+        im->bands = im->pixelsize = 4;
+        im->linesize = xsize * 4;
+
     } else if (strcmp(mode, "CMYK") == 0) {
         /* 32-bit colour separation */
         im->bands = im->pixelsize = 4;

libImaging/Unpack.c

@@ -747,6 +747,30 @@ unpackRGBa(UINT8* out, const UINT8* in, int pixels)
     }
 }
 
+static void
+unpackBGRa(UINT8* out, const UINT8* in, int pixels)
+{
+    int i;
+    /* premultiplied BGRA */
+    for (i = 0; i < pixels; i++) {
+        int a = in[3];
+        if (!a)
+            out[R] = out[G] = out[B] = out[A] = 0;
+        else if (a == 255) {
+            out[R] = in[2];
+            out[G] = in[1];
+            out[B] = in[0];
+            out[A] = a;
+        } else {
+            out[R] = CLIP(in[2] * 255 / a);
+            out[G] = CLIP(in[1] * 255 / a);
+            out[B] = CLIP(in[0] * 255 / a);
+            out[A] = a;
+        }
+        out += 4; in += 4;
+    }
+}
+
 static void
 unpackRGBAI(UINT8* out, const UINT8* in, int pixels)
 {
@@ -1206,6 +1230,7 @@ static struct {
     {"RGBA",    "LA;16B",       32,     unpackRGBALA16B},
     {"RGBA",    "RGBA",         32,     copy4},
     {"RGBA",    "RGBa",         32,     unpackRGBa},
+    {"RGBA",    "BGRa",         32,     unpackBGRa},
     {"RGBA",    "RGBA;I",       32,     unpackRGBAI},
     {"RGBA",    "RGBA;L",       32,     unpackRGBAL},
     {"RGBA",    "RGBA;15",      16,     ImagingUnpackRGBA15},
@@ -1226,6 +1251,7 @@ static struct {
     {"RGBa",    "BGRa",         32,     unpackBGRA},
     {"RGBa",    "aRGB",         32,     unpackARGB},
     {"RGBa",    "aBGR",         32,     unpackABGR},
+    {"BGRa",    "BGRa",         32,     copy4},
 
     /* true colour w. padding */
     {"RGBX",    "RGB",          24,     ImagingUnpackRGB},