Add option to renormalize mipmaps when generating them for normalmaps.

Reduces some aliasing.

core/image.cpp

@@ -937,7 +937,7 @@ bool Image::_can_modify(Format p_format) const {
 	return p_format <= FORMAT_RGBE9995;
 }
 
-template <int CC>
+template <int CC, bool renormalize>
 static void _generate_po2_mipmap(const uint8_t *p_src, uint8_t *p_dst, uint32_t p_width, uint32_t p_height) {
 
 	//fast power of 2 mipmap generation
@@ -963,6 +963,19 @@ static void _generate_po2_mipmap(const uint8_t *p_src, uint8_t *p_dst, uint32_t
 				dst_ptr[j] = val >> 2;
 			}
 
+			if (renormalize) {
+				Vector3 n(dst_ptr[0] / 255.0, dst_ptr[1] / 255.0, dst_ptr[2] / 255.0);
+				n *= 2.0;
+				n -= Vector3(1, 1, 1);
+				n.normalize();
+				n += Vector3(1, 1, 1);
+				n *= 0.5;
+				n *= 255;
+				dst_ptr[0] = CLAMP(int(n.x), 0, 255);
+				dst_ptr[1] = CLAMP(int(n.y), 0, 255);
+				dst_ptr[2] = CLAMP(int(n.z), 0, 255);
+			}
+
 			dst_ptr += CC;
 			rup_ptr += CC * 2;
 			rdown_ptr += CC * 2;
@@ -1045,11 +1058,11 @@ void Image::shrink_x2() {
 			switch (format) {
 
 				case FORMAT_L8:
-				case FORMAT_R8: _generate_po2_mipmap<1>(r.ptr(), w.ptr(), width, height); break;
-				case FORMAT_LA8: _generate_po2_mipmap<2>(r.ptr(), w.ptr(), width, height); break;
-				case FORMAT_RG8: _generate_po2_mipmap<2>(r.ptr(), w.ptr(), width, height); break;
-				case FORMAT_RGB8: _generate_po2_mipmap<3>(r.ptr(), w.ptr(), width, height); break;
-				case FORMAT_RGBA8: _generate_po2_mipmap<4>(r.ptr(), w.ptr(), width, height); break;
+				case FORMAT_R8: _generate_po2_mipmap<1, false>(r.ptr(), w.ptr(), width, height); break;
+				case FORMAT_LA8: _generate_po2_mipmap<2, false>(r.ptr(), w.ptr(), width, height); break;
+				case FORMAT_RG8: _generate_po2_mipmap<2, false>(r.ptr(), w.ptr(), width, height); break;
+				case FORMAT_RGB8: _generate_po2_mipmap<3, false>(r.ptr(), w.ptr(), width, height); break;
+				case FORMAT_RGBA8: _generate_po2_mipmap<4, false>(r.ptr(), w.ptr(), width, height); break;
 				default: {}
 			}
 		}
@@ -1060,7 +1073,7 @@ void Image::shrink_x2() {
 	}
 }
 
-Error Image::generate_mipmaps() {
+Error Image::generate_mipmaps(bool p_renormalize) {
 
 	if (!_can_modify(format)) {
 		ERR_EXPLAIN("Cannot generate mipmaps in indexed, compressed or custom image formats.");
@@ -1089,11 +1102,22 @@ Error Image::generate_mipmaps() {
 		switch (format) {
 
 			case FORMAT_L8:
-			case FORMAT_R8: _generate_po2_mipmap<1>(&wp[prev_ofs], &wp[ofs], prev_w, prev_h); break;
+			case FORMAT_R8: _generate_po2_mipmap<1, false>(&wp[prev_ofs], &wp[ofs], prev_w, prev_h); break;
 			case FORMAT_LA8:
-			case FORMAT_RG8: _generate_po2_mipmap<2>(&wp[prev_ofs], &wp[ofs], prev_w, prev_h); break;
-			case FORMAT_RGB8: _generate_po2_mipmap<3>(&wp[prev_ofs], &wp[ofs], prev_w, prev_h); break;
-			case FORMAT_RGBA8: _generate_po2_mipmap<4>(&wp[prev_ofs], &wp[ofs], prev_w, prev_h); break;
+			case FORMAT_RG8: _generate_po2_mipmap<2, false>(&wp[prev_ofs], &wp[ofs], prev_w, prev_h); break;
+			case FORMAT_RGB8:
+				if (p_renormalize)
+					_generate_po2_mipmap<3, true>(&wp[prev_ofs], &wp[ofs], prev_w, prev_h);
+				else
+					_generate_po2_mipmap<3, false>(&wp[prev_ofs], &wp[ofs], prev_w, prev_h);
+
+				break;
+			case FORMAT_RGBA8:
+				if (p_renormalize)
+					_generate_po2_mipmap<4, true>(&wp[prev_ofs], &wp[ofs], prev_w, prev_h);
+				else
+					_generate_po2_mipmap<4, false>(&wp[prev_ofs], &wp[ofs], prev_w, prev_h);
+				break;
 			default: {}
 		}
 
@@ -2217,7 +2241,7 @@ void Image::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("crop", "width", "height"), &Image::crop);
 	ClassDB::bind_method(D_METHOD("flip_x"), &Image::flip_x);
 	ClassDB::bind_method(D_METHOD("flip_y"), &Image::flip_y);
-	ClassDB::bind_method(D_METHOD("generate_mipmaps"), &Image::generate_mipmaps);
+	ClassDB::bind_method(D_METHOD("generate_mipmaps", "renormalize"), &Image::generate_mipmaps, DEFVAL(false));
 	ClassDB::bind_method(D_METHOD("clear_mipmaps"), &Image::clear_mipmaps);
 
 	ClassDB::bind_method(D_METHOD("create", "width", "height", "use_mipmaps", "format"), &Image::_create_empty);

core/image.h

@@ -217,7 +217,7 @@ public:
 	/**
 	 * Generate a mipmap to an image (creates an image 1/4 the size, with averaging of 4->1)
 	 */
-	Error generate_mipmaps();
+	Error generate_mipmaps(bool p_renormalize = false);
 
 	void clear_mipmaps();
 

editor/import/resource_importer_texture.cpp

@@ -295,7 +295,7 @@ void ResourceImporterTexture::_save_stex(const Ref<Image> &p_image, const String
 		case COMPRESS_VIDEO_RAM: {
 
 			Ref<Image> image = p_image->duplicate();
-			image->generate_mipmaps();
+			image->generate_mipmaps(p_force_normal);
 
 			if (p_force_rgbe && image->get_format() >= Image::FORMAT_R8 && image->get_format() <= Image::FORMAT_RGBE9995) {
 				image->convert(Image::FORMAT_RGBE9995);