Fix Texture3D import not working

Fix Texture3D import not working when texture has fully opaque and (partly or fully) transparent slices.

For better style make cases of detect_alpha check against the exact enums rather than the enum 0.

drivers/png/png_driver_common.cpp

@@ -153,7 +153,7 @@ Error image_to_png(const Ref<Image> &p_image, Vector<uint8_t> &p_buffer) {
 			png_img.format = PNG_FORMAT_RGBA;
 			break;
 		default:
-			if (source_image->detect_alpha()) {
+			if (source_image->detect_alpha() != Image::ALPHA_NONE) {
 				source_image->convert(Image::FORMAT_RGBA8);
 				png_img.format = PNG_FORMAT_RGBA;
 			} else {

editor/import/resource_importer_layered_texture.cpp

@@ -343,7 +343,7 @@ Error ResourceImporterLayeredTexture::import(ResourceUID::ID p_source_id, const
 		//if using video ram, optimize
 		if (channel_pack == 0) {
 			//remove alpha if not needed, so compression is more efficient
-			if (image->get_format() == Image::FORMAT_RGBA8 && !image->detect_alpha()) {
+			if (image->get_format() == Image::FORMAT_RGBA8 && image->detect_alpha() == Image::ALPHA_NONE) {
 				image->convert(Image::FORMAT_RGB8);
 			}
 		} else if (image->get_format() < Image::FORMAT_RGBA8) {
@@ -487,6 +487,7 @@ ResourceImporterLayeredTexture::~ResourceImporterLayeredTexture() {
 void ResourceImporterLayeredTexture::_check_compress_ctex(const String &p_source_file, Ref<LayeredTextureImport> r_texture_import) {
 	String extension = get_save_extension();
 	ERR_FAIL_NULL(r_texture_import->csource);
+
 	if (r_texture_import->compress_mode != COMPRESS_VRAM_COMPRESSED) {
 		// Import normally.
 		_save_tex(*r_texture_import->slices, r_texture_import->save_path + "." + extension, r_texture_import->compress_mode, r_texture_import->lossy, Image::COMPRESS_S3TC /* IGNORED */, *r_texture_import->csource, r_texture_import->used_channels, r_texture_import->mipmaps, false);

modules/webp/webp_common.cpp

@@ -63,7 +63,7 @@ Vector<uint8_t> _webp_packer(const Ref<Image> &p_image, float p_quality, bool p_
 		Error error = img->decompress();
 		ERR_FAIL_COND_V_MSG(error != OK, Vector<uint8_t>(), "Couldn't decompress image.");
 	}
-	if (img->detect_alpha()) {
+	if (img->detect_alpha() != Image::ALPHA_NONE) {
 		img->convert(Image::FORMAT_RGBA8);
 	} else {
 		img->convert(Image::FORMAT_RGB8);

scene/resources/compressed_texture.cpp

@@ -313,8 +313,6 @@ Ref<Image> CompressedTexture2D::load_image_from_file(Ref<FileAccess> f, int p_si
 		Vector<Ref<Image>> mipmap_images;
 		uint64_t total_size = 0;
 
-		bool first = true;
-
 		for (uint32_t i = 0; i < mipmaps + 1; i++) {
 			uint32_t size = f->get_32();
 
@@ -339,18 +337,20 @@ Ref<Image> CompressedTexture2D::load_image_from_file(Ref<FileAccess> f, int p_si
 			} else if (data_format == DATA_FORMAT_WEBP && Image::webp_unpacker) {
 				img = Image::webp_unpacker(pv);
 			}
-
 			if (img.is_null() || img->is_empty()) {
 				ERR_FAIL_COND_V(img.is_null() || img->is_empty(), Ref<Image>());
 			}
-
-			if (first) {
-				//format will actually be the format of the first image,
-				//as it may have changed on compression
-				format = img->get_format();
-				first = false;
-			} else if (img->get_format() != format) {
-				img->convert(format); //all needs to be the same format
+			// If the image is compressed and its format doesn't match the desired format, return an empty reference.
+			// This is done to avoid recompressing the image on load.
+			ERR_FAIL_COND_V(img->is_compressed() && format != img->get_format(), Ref<Image>());
+
+			// The format will actually be the format of the header,
+			// as it may have changed on compression.
+			if (!img->is_compressed() && format != img->get_format()) {
+				// Convert the image to the desired format.
+				// Note: We are not decompressing the image here, just changing its format.
+				// It's important that all images in the texture array share the same format for correct rendering.
+				img->convert(format);
 			}
 
 			total_size += img->get_data().size();