2 files changed, 81 insertions, 0 deletions

diff --git a/graphics/surface.cpp b/graphics/surface.cpp
index c0f1046eae..1604eaa488 100644
--- a/graphics/surface.cpp
+++ b/graphics/surface.cpp
@@ -26,6 +26,7 @@
 #include "common/textconsole.h"
 #include "graphics/primitives.h"
 #include "graphics/surface.h"
+#include "graphics/conversion.h"
 
 namespace Graphics {
 
@@ -271,6 +272,72 @@ void Surface::move(int dx, int dy, int height) {
 	}
 }
 
+void Surface::convertToInPlace(const PixelFormat &dstFormat, const byte *palette) {
+	// Do not convert to the same format and ignore empty surfaces.
+	if (format == dstFormat || pixels == 0) {
+		return;
+	}
+
+	if (format.bytesPerPixel == 0 || format.bytesPerPixel > 4)
+		error("Surface::convertToInPlace(): Can only convert from 1Bpp, 2Bpp, 3Bpp, and 4Bpp");
+
+	if (dstFormat.bytesPerPixel != 2 && dstFormat.bytesPerPixel != 4)
+		error("Surface::convertToInPlace(): Can only convert to 2Bpp and 4Bpp");
+
+	// In case the surface data needs more space allocate it.
+	if (dstFormat.bytesPerPixel > format.bytesPerPixel) {
+		void *const newPixels = realloc(pixels, w * h * dstFormat.bytesPerPixel);
+		if (!newPixels) {
+			error("Surface::convertToInPlace(): Out of memory");
+		}
+		pixels = newPixels;
+	}
+
+	// We take advantage of the fact that pitch is always w * format.bytesPerPixel.
+	// This is assured by the logic of Surface::create.
+
+	// We need to handle 1 Bpp surfaces special here.
+	if (format.bytesPerPixel == 1) {
+		assert(palette);
+
+		for (int y = h; y > 0; --y) {
+			const byte *srcRow = (const byte *)pixels + y * pitch - 1;
+			byte *dstRow = (byte *)pixels + y * w * dstFormat.bytesPerPixel - dstFormat.bytesPerPixel;
+
+			for (int x = 0; x < w; x++) {
+				byte index = *srcRow--;
+				byte r = palette[index * 3];
+				byte g = palette[index * 3 + 1];
+				byte b = palette[index * 3 + 2];
+
+				uint32 color = dstFormat.RGBToColor(r, g, b);
+
+				if (dstFormat.bytesPerPixel == 2)
+					*((uint16 *)dstRow) = color;
+				else
+					*((uint32 *)dstRow) = color;
+
+				dstRow -= dstFormat.bytesPerPixel;
+			}
+		}
+	} else {
+		crossBlit((byte *)pixels, (const byte *)pixels, w * dstFormat.bytesPerPixel, pitch, w, h, dstFormat, format);
+	}
+
+	// In case the surface data got smaller, free up some memory.
+	if (dstFormat.bytesPerPixel < format.bytesPerPixel) {
+		void *const newPixels = realloc(pixels, w * h * dstFormat.bytesPerPixel);
+		if (!newPixels) {
+			error("Surface::convertToInPlace(): Freeing memory failed");
+		}
+		pixels = newPixels;
+	}
+
+	// Update the surface specific data.
+	format = dstFormat;
+	pitch = w * dstFormat.bytesPerPixel;
+}
+
 Graphics::Surface *Surface::convertTo(const PixelFormat &dstFormat, const byte *palette) const {
 	assert(pixels);
 
diff --git a/graphics/surface.h b/graphics/surface.h
index eb8d1ac42e..eaf62f84eb 100644
--- a/graphics/surface.h
+++ b/graphics/surface.h
@@ -137,6 +137,20 @@ struct Surface {
 	/**
 	 * Convert the data to another pixel format.
 	 *
+	 * This works in-place. This means it will not create an additional buffer
+	 * for the conversion process. The value of pixels might change though.
+	 *
+	 * Note that you should only use this, when you created the Surface data via
+	 * create! Otherwise this function has undefined behavior.
+	 *
+	 * @param dstFormat The desired format
+	 * @param palette   The palette (in RGB888), if the source format has a Bpp of 1
+	 */
+	void convertToInPlace(const PixelFormat &dstFormat, const byte *palette = 0);
+
+	/**
+	 * Convert the data to another pixel format.
+	 *
 	 * The calling code must call free on the returned surface and then delete
 	 * it.
 	 *