收口颜色格式，删除原来的 RGBA8888 的存储和调用

tests/render_pipeline_tests.cpp

@@ -53,6 +53,21 @@ namespace
 		assert(pixels[1] == 0xF800u);
 	}
 
+	void TestImageDefaultsToRgba5551AndReturnsRawPixels()
+	{
+		const uint16_t default_pixels[] = { 0xF801u, 0x0000u };
+		RenderData::Image default_image(default_pixels, 1, 1);
+		assert(default_image.format == RenderData::PixelFormat::RGBA5551);
+
+		const uint16_t explicit_pixels[] = { 0x07C1u };
+		RenderData::Image explicit_image(
+			explicit_pixels,
+			1,
+			1,
+			RenderData::PixelFormat::RGBA5551);
+		assert(explicit_image.get_pixel(0, 0) == 0x07C1u);
+	}
+
 	void TestDrawSpriteUsesOneBitAlpha()
 	{
 		const uint16_t sprite_pixels[] = {
@@ -199,6 +214,7 @@ int main()
 {
 	TestFramePixelIsRgb565();
 	TestFrameBufferStoresRgb565();
+	TestImageDefaultsToRgba5551AndReturnsRawPixels();
 	TestDrawSpriteUsesOneBitAlpha();
 	TestSpriteAssetLoaderRoundTripsRgba5551();
 	TestDrawTextUsesBitMaskAndColor();