Nearest Neighbor Color Removal (#2281)

* Use nearest neighbor to set alpha of removed color from images like GM8.1
* Give each sprite frame its own bottom-left transparency pixel like GM8.1
* Use removed color instead of black in transparent areas like GM8.1
* Ensure isolated pixels are always visible like GM8.1

ENIGMAsystem/SHELL/Graphics_Systems/General/GSscreen.cpp

@@ -73,10 +73,7 @@ RawImage create_from_screen_helper(int x, int y, int w, int h, bool removeback,
   if (flipped)
     enigma::image_flip(i);
 
-  if (removeback) {
-    Color c = enigma::image_get_pixel_color(i, 0, h - 1);
-    enigma::image_swap_color(i, c, Color {0, 0, 0, 0});
-  }
+  if (removeback) enigma::image_remove_color(i);
 
   return i;
 }

ENIGMAsystem/SHELL/Graphics_Systems/General/GSsurface.cpp

@@ -378,10 +378,7 @@ int background_create_from_surface(int id, int x, int y, int w, int h, bool remo
 
   enigma::RawImage s(enigma::graphics_copy_texture_pixels(base.texture,x,y,w,h), w, h);
 
-  if (removeback) {
-    enigma::Color c = enigma::image_get_pixel_color(s, 0, h - 1);
-    enigma::image_swap_color(s, c, enigma::Color {0, 0, 0, 0});
-  }
+  if (removeback) enigma::image_remove_color(s);
 
   unsigned fullwidth, fullheight;
   int texID = enigma::graphics_create_texture(s, false, &fullwidth, &fullheight);

ENIGMAsystem/SHELL/Universal_System/Resources/backgrounds.cpp

@@ -54,10 +54,7 @@ Background background_add_helper(std::string filename, bool transparent, bool sm
 
   // If background is transparent, set the alpha to zero for pixels that should be
   // transparent from lower left pixel color
-  if (transparent) {
-    Color c = enigma::image_get_pixel_color(imgs[0], 0, imgs[0].h - 1);
-    enigma::image_swap_color(imgs[0], c, Color {0, 0, 0, 0});
-  }
+  if (transparent) enigma::image_remove_color(imgs[0]);
 
   nb.textureID = graphics_create_texture(imgs[0], mipmap, &fullwidth, &fullheight);
   nb.textureBounds = TexRect(0, 0, static_cast<gs_scalar>(imgs[0].w) / fullwidth, static_cast<gs_scalar>(imgs[0].h) / fullheight);

ENIGMAsystem/SHELL/Universal_System/Resources/sprites.cpp

@@ -45,25 +45,17 @@ Sprite sprite_add_helper(std::string filename, int imgnumb, bool precise, bool t
   unsigned cellwidth = ((imgs.size() > 1) ? imgs[0].w : imgs[0].w / imgnumb);
   Sprite ns(cellwidth, imgs[0].h, x_offset, y_offset);
   ns.SetBBox(0, 0, cellwidth, imgs[0].h);
-
-  // If sprite transparent, set the alpha to zero for pixels that should be
-  // transparent from lower left pixel color
-  Color c = enigma::image_get_pixel_color(imgs[0], 0, imgs[0].h - 1);
 
   if (imgs.size() == 1 && imgnumb > 1) {
-    if (transparent) {      
-      enigma::image_swap_color(imgs[0], c, Color {0, 0, 0, 0});
-    }
+    if (transparent) enigma::image_remove_color(imgs[0]);
 
     std::vector<RawImage> rawSubimages = enigma::image_split(imgs[0], imgnumb);
     for (const RawImage& i : rawSubimages) {
       ns.AddSubimage(i, ((precise) ? enigma::ct_precise : enigma::ct_bbox), i.pxdata, mipmap);
     }
   } else {
     for (RawImage& i : imgs) {
-      if (transparent) {
-        enigma::image_swap_color(i, c, Color {0, 0, 0, 0});
-      }
+      if (transparent) enigma::image_remove_color(i);
       ns.AddSubimage(i, ((precise) ? enigma::ct_precise : enigma::ct_bbox), i.pxdata, mipmap);
     }
   }

ENIGMAsystem/SHELL/Universal_System/image_formats.cpp

@@ -87,6 +87,56 @@ void image_swap_color(RawImage& in, Color oldColor, Color newColor) {
   }
 }
 
+void image_remove_color(RawImage& in, Color oldColor) {
+  #ifdef DEBUG_MODE
+  if (in.pxdata == nullptr) {
+    in.pxdata = new unsigned char[in.w * in.h * 4];
+    std::fill(in.pxdata, in.pxdata + (in.w * in.h * 4), 255);
+    DEBUG_MESSAGE("Attempt to access a null pointer" , MESSAGE_TYPE::M_ERROR);
+    return;
+  }
+  #endif
+
+  unsigned int ih, iw;
+  for (ih = 0; ih < in.h; ih++) {
+    int index = ih * in.w * 4;
+
+    for (iw = 0; iw < in.w; iw++) {
+      if (
+           in.pxdata[index]     == oldColor.b
+        && in.pxdata[index + 1] == oldColor.g
+        && in.pxdata[index + 2] == oldColor.r
+        ) {
+          in.pxdata[index + 3] = 0;
+      } else {
+        unsigned int nw = (iw <= 0 ? iw : iw - 1),
+                     nh = (ih <= 0 ? ih : ih - 1);
+        float neighbors = 0, counted = 0;
+        for (; nh <= ih + 1 && nh < in.h; ++nh) {
+          for (; nw <= iw + 1 && nw < in.w; ++nw) {
+            ++counted;
+            int ni = (nh * in.w + nw) * 4;
+            if (
+                 in.pxdata[ni]     != oldColor.b
+              || in.pxdata[ni + 1] != oldColor.g
+              || in.pxdata[ni + 2] != oldColor.r
+              )
+              ++neighbors;
+          }
+        }
+        in.pxdata[index + 3] = static_cast<unsigned char>((neighbors/counted) * 255.0f);
+      }
+
+      index += 4;
+    }
+  }
+}
+
+void image_remove_color(RawImage& in) {
+  Color bottom_left = image_get_pixel_color(in, 0, in.h - 1);
+  image_remove_color(in, bottom_left);
+}
+
 std::vector<RawImage> image_split(const RawImage& in, unsigned imgcount) {
   std::vector<RawImage> imgs(imgcount);
   unsigned splitWidth = in.w / imgcount;

ENIGMAsystem/SHELL/Universal_System/image_formats.h

@@ -60,6 +60,8 @@ enum {
 
 Color image_get_pixel_color(const RawImage& in, unsigned x, unsigned y);
 void image_swap_color(RawImage& in, Color oldColor, Color newColor);
+void image_remove_color(RawImage& in, Color oldColor);
+void image_remove_color(RawImage& in);
 /// Note splits horizontally
 std::vector<RawImage> image_split(const RawImage& in, unsigned imgcount);
 RawImage image_pad(const RawImage& in, unsigned newWidth, unsigned newHeight);