From 803665404e3fbd937f3fcd88a1c363496b4baa11 Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Sun, 24 Jul 2016 23:53:08 +0000
Subject: [PATCH] Add support for BGR formats to Pixmap, and RGB conversion.

The Cairo image surface backend uses the BGR format for "RGB24"
for some reason, and we need to handle that.
---
 src/render/rendergl1.cpp |  3 +++
 src/resource.cpp         | 52 +++++++++++++++++++++++++++++++++++++---
 src/resource.h           |  4 +++-
 3 files changed, 55 insertions(+), 4 deletions(-)

diff --git a/src/render/rendergl1.cpp b/src/render/rendergl1.cpp
index b08a2548..1864adfd 100644
--- a/src/render/rendergl1.cpp
+++ b/src/render/rendergl1.cpp
@@ -216,6 +216,9 @@ void OpenGl1Renderer::SelectTexture(std::shared_ptr<const Pixmap> pm) {
         case Pixmap::Format::RGBA: format = GL_RGBA;  break;
         case Pixmap::Format::RGB:  format = GL_RGB;   break;
         case Pixmap::Format::A:    format = GL_ALPHA; break;
+        case Pixmap::Format::BGRA:
+        case Pixmap::Format::BGR:
+            ssassert(false, "Unexpected pixmap format");
     }
     glTexImage2D(GL_TEXTURE_2D, 0, format, pm->width, pm->height, 0,
                  format, GL_UNSIGNED_BYTE, &pm->data[0]);
diff --git a/src/resource.cpp b/src/resource.cpp
index b5be2724..107047e3 100644
--- a/src/resource.cpp
+++ b/src/resource.cpp
@@ -65,7 +65,9 @@ std::shared_ptr<Pixmap> LoadPng(const std::string &name) {
 size_t Pixmap::GetBytesPerPixel() const {
     switch(format) {
         case Format::RGBA: return 4;
+        case Format::BGRA: return 4;
         case Format::RGB:  return 3;
+        case Format::BGR:  return 3;
         case Format::A:    return 1;
     }
     ssassert(false, "Unexpected pixmap format");
@@ -81,12 +83,52 @@ RgbaColor Pixmap::GetPixel(size_t x, size_t y) const {
         case Format::RGB:
             return RgbaColor::From(pixel[0], pixel[1], pixel[2],      255);
 
+        case Format::BGRA:
+            return RgbaColor::From(pixel[2], pixel[1], pixel[0], pixel[3]);
+
+        case Format::BGR:
+            return RgbaColor::From(pixel[2], pixel[1], pixel[0],      255);
+
         case Format::A:
             return RgbaColor::From(     255,      255,      255, pixel[0]);
     }
     ssassert(false, "Unexpected resource format");
 }
 
+void Pixmap::ConvertTo(Format newFormat) {
+    switch(format) {
+        case Format::RGBA:
+            ssassert(newFormat == Format::BGRA, "Unexpected target format");
+            break;
+
+        case Format::BGRA:
+            ssassert(newFormat == Format::RGBA, "Unexpected target format");
+            break;
+
+        case Format::RGB:
+            ssassert(newFormat == Format::BGR, "Unexpected target format");
+            break;
+
+        case Format::BGR:
+            ssassert(newFormat == Format::RGB, "Unexpected target format");
+            break;
+
+        case Format::A:
+            ssassert(false, "Unexpected target format");
+    }
+
+    size_t bpp = GetBytesPerPixel();
+    for(size_t j = 0; j != height; j++) {
+        uint8_t *row = &data[j * stride];
+        for(size_t i = 0; i != width * bpp; i += bpp) {
+            // This handles both RGB<>BGR and RGBA<>BGRA.
+            std::swap(row[i], row[i + 2]);
+        }
+    }
+
+    format = newFormat;
+}
+
 static std::shared_ptr<Pixmap> ReadPngIntoPixmap(png_struct *png_ptr, png_info *info_ptr,
                                                  bool flip) {
     png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_EXPAND | PNG_TRANSFORM_GRAY_TO_RGB, NULL);
@@ -175,10 +217,13 @@ exit:
 
 bool Pixmap::WritePng(FILE *f, bool flip) {
     int colorType;
+    bool bgr;
     switch(format) {
-        case Format::RGBA: colorType = PNG_COLOR_TYPE_RGBA; break;
-        case Format::RGB:  colorType = PNG_COLOR_TYPE_RGB;  break;
-        case Format::A:    ssassert(false, "Unexpected pixmap format");
+        case Format::RGBA: colorType = PNG_COLOR_TYPE_RGBA; bgr = false; break;
+        case Format::BGRA: colorType = PNG_COLOR_TYPE_RGBA; bgr = true;  break;
+        case Format::RGB:  colorType = PNG_COLOR_TYPE_RGB;  bgr = false; break;
+        case Format::BGR:  colorType = PNG_COLOR_TYPE_RGB;  bgr = true;  break;
+        case Format::A:    colorType = PNG_COLOR_TYPE_GRAY; bgr = false; break;
     }
 
     std::vector<uint8_t *> rows;
@@ -204,6 +249,7 @@ bool Pixmap::WritePng(FILE *f, bool flip) {
     png_set_IHDR(png_ptr, info_ptr, width, height, 8,
                  colorType, PNG_INTERLACE_NONE,
                  PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+    if(bgr) png_set_bgr(png_ptr);
     png_write_info(png_ptr, info_ptr);
     png_write_image(png_ptr, &rows[0]);
     png_write_end(png_ptr, info_ptr);
diff --git a/src/resource.h b/src/resource.h
index aab95069..787e2a1f 100644
--- a/src/resource.h
+++ b/src/resource.h
@@ -24,7 +24,7 @@ std::shared_ptr<Pixmap> LoadPng(const std::string &name);
 
 class Pixmap {
 public:
-    enum class Format { RGBA, RGB, A };
+    enum class Format { BGRA, RGBA, BGR, RGB, A };
 
     Format                     format;
     size_t                     width;
@@ -40,6 +40,8 @@ public:
 
     size_t GetBytesPerPixel() const;
     RgbaColor GetPixel(size_t x, size_t y) const;
+
+    void ConvertTo(Format newFormat);
 };
 
 class BitmapFont {