implement color mixing

Laguna1989 · Oct 10, 2023 · ef11022 · ef11022
1 parent 82682d0
commit ef11022
Showing 1 changed file with 44 additions and 1 deletion.
diff --git a/impl/aselib/image_builder.cpp b/impl/aselib/image_builder.cpp
@@ -1,5 +1,45 @@
 #include "image_builder.hpp"
 
+namespace {
+aselib::PixelDataRGBA addPixelColor(
+    aselib::PixelDataRGBA const& pixel_src, aselib::PixelDataRGBA const& pixel_orig)
+{
+
+    if (pixel_src.a == 255) {
+        // just paint over
+        return pixel_src;
+    } else if (pixel_src.a == 0) {
+        return pixel_orig;
+    } else {
+        // TODO test
+
+        float const a0 = static_cast<float>(pixel_src.a) / 255.0f;
+        float const r0 = static_cast<float>(pixel_src.r) / 255.0f;
+        float const g0 = static_cast<float>(pixel_src.g) / 255.0f;
+        float const b0 = static_cast<float>(pixel_src.b) / 255.0f;
+
+        float const a1 = static_cast<float>(pixel_orig.a) / 255.0f;
+        float const r1 = static_cast<float>(pixel_orig.r) / 255.0f;
+        float const g1 = static_cast<float>(pixel_orig.g) / 255.0f;
+        float const b1 = static_cast<float>(pixel_orig.b) / 255.0f;
+
+        float const a01 = (1.0f - a0) * a1 + a0;
+        float const r01 = ((1.0f - a0) * a1 * r1 + a0 * r0) / a01;
+        float const g01 = ((1.0f - a0) * a1 * g1 + a0 * g0) / a01;
+        float const b01 = ((1.0f - a0) * a1 * b1 + a0 * b0) / a01;
+
+        return aselib::PixelDataRGBA {
+            // clang-format off
+            static_cast<std::uint8_t>(r01 * 255.0f),
+            static_cast<std::uint8_t>(g01 * 255.0f),
+            static_cast<std::uint8_t>(b01 * 255.0f),
+            static_cast<std::uint8_t>(a01 * 255.0f)
+            // clang-format on
+        };
+    }
+}
+} // namespace
+
 aselib::Image aselib::makeImageFromAse(aselib::AsepriteData const& ase)
 {
     Image img {};
@@ -29,7 +69,10 @@ aselib::Image aselib::makeImageFromAse(aselib::AsepriteData const& ase)
 
                     auto const& pixel_src
                         = cel.m_pixels_rgba[x_in_cel + y_in_cel * cel.m_cell_width];
-                    img.getPixelAt(x_in_frame + frame_offset_x, y_in_frame) = pixel_src;
+                    auto const& pixel_orig
+                        = img.getPixelAt(x_in_frame + frame_offset_x, y_in_frame);
+                    img.getPixelAt(x_in_frame + frame_offset_x, y_in_frame)
+                        = addPixelColor(pixel_src, pixel_orig);
                 }
             }
         }