init

shaders/oit_depth_peeling/background.frag

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+#version 450
+/* Copyright (c) 2024, Google
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 the "License";
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *	 http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+layout (location = 0) in vec2 inUV;
+
+////////////////////////////////////////
+
+layout(set = 0, binding = 0) uniform SceneConstants
+{
+	mat4  model_view_projection;
+	float background_grayscale;
+	float object_alpha;
+	int   front_layer_index;
+	int   back_layer_index;
+} sceneConstants;
+
+////////////////////////////////////////
+
+layout(set = 0, binding = 1) uniform sampler2D backgroundTex;
+
+////////////////////////////////////////
+
+layout(location = 0) out vec4 outColor;
+
+void main()
+{
+	outColor = texture(backgroundTex, inUV) * sceneConstants.background_grayscale;
+}
+

shaders/oit_depth_peeling/combine.frag

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+#version 450
+/* Copyright (c) 2024, Google
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 the "License";
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *	 http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+layout (location = 0) in vec2 inUV;
+
+layout (location = 0) out vec4 outFragColor;
+
+////////////////////////////////////////
+
+layout(set = 0, binding = 0) uniform SceneConstants
+{
+	mat4  model_view_projection;
+	float background_grayscale;
+	float object_alpha;
+	int   front_layer_index;
+	int   back_layer_index;
+} sceneConstants;
+
+const int kLayersCount = 8;
+layout(set = 0, binding = 2) uniform sampler2D layerTex[kLayersCount];
+
+////////////////////////////////////////
+
+void main()
+{
+	// Merge all layers using in-shader alpha blending.
+	vec4 color = vec4(0.0f, 0.0f, 0.0f, 1.0f);
+	const int front_layer_index = clamp(sceneConstants.front_layer_index, 0, kLayersCount - 1);
+	const int back_layer_index = clamp(sceneConstants.back_layer_index, front_layer_index, kLayersCount - 1);
+	for(int i = back_layer_index; i >= front_layer_index; --i)
+	{
+		const vec4 fragmentColor = texture(layerTex[i], inUV);
+		color.rgb = mix(color.rgb, fragmentColor.rgb, fragmentColor.a);
+		color.a *= 1.0f - fragmentColor.a;
+	}
+	// The final color is blended in the background using fixed-function alpha blending.
+	color.a = 1.0f - color.a;
+	outFragColor = color;
+}
+

shaders/oit_depth_peeling/fullscreen.vert

@@ -0,0 +1,35 @@
+#version 450
+/* Copyright (c) 2024, Google
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 the "License";
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *	 http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+layout (location = 0) out vec2 outUV;
+
+////////////////////////////////////////
+
+void main()
+{
+	const vec4 fullscreen_triangle[] =
+	{
+		vec4(-1.0f,  3.0f, 0.0f, 2.0f),
+		vec4(-1.0f, -1.0f, 0.0f, 0.0f),
+		vec4( 3.0f, -1.0f, 2.0f, 0.0f),
+	};
+	const vec4 vertex = fullscreen_triangle[gl_VertexIndex % 3];
+	gl_Position = vec4(vertex.xy, 0.0f, 1.0f);
+	outUV = vertex.zw;
+}
+

shaders/oit_depth_peeling/gather.frag

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+#version 450
+/* Copyright (c) 2024, Google
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 the "License";
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *	 http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+layout (location = 0) in vec4 inColor;
+
+layout (location = 0) out vec4 outFragColor;
+
+////////////////////////////////////////
+
+layout(set = 0, binding = 1) uniform sampler2D depthTex;
+
+////////////////////////////////////////
+
+void main()
+{
+	// 'depthTex' contains the depth information of the previous layer.
+	// That information is used to discard any fragment that belongs to
+	// a layer that has already be rendered (i.e. a layer further in front).
+	const float layerDepth = texelFetch(depthTex, ivec2(gl_FragCoord.xy), 0).r;
+	if(gl_FragCoord.z >= layerDepth)
+	{
+		// NOTE
+		// Remember that a reversed Z-buffer is used here.
+		// Fragments closer to the camera have a higher z coordinate.
+		discard;
+	}
+
+	outFragColor = inColor;
+}
+

shaders/oit_depth_peeling/gather.vert

@@ -0,0 +1,42 @@
+#version 450
+/* Copyright (c) 2024, Google
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 the "License";
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *	 http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+layout (location = 0) in vec3 inPos;
+layout (location = 1) in vec2 inUV;
+
+layout (location = 0) out vec4 outColor;
+
+////////////////////////////////////////
+
+layout(set = 0, binding = 0) uniform SceneConstants
+{
+	mat4  model_view_projection;
+	float background_grayscale;
+	float object_alpha;
+	int   front_layer_index;
+	int   back_layer_index;
+} sceneConstants;
+
+////////////////////////////////////////
+
+void main()
+{
+	gl_Position = sceneConstants.model_view_projection * vec4(inPos, 1.0f);
+	outColor = vec4(inUV, 0.0f, sceneConstants.object_alpha);
+}
+

shaders/oit_depth_peeling/gather_first.frag

@@ -0,0 +1,31 @@
+#version 450
+/* Copyright (c) 2024, Google
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 the "License";
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *	 http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+layout (location = 0) in vec4 inColor;
+
+layout (location = 0) out vec4 outFragColor;
+
+////////////////////////////////////////
+
+void main()
+{
+	// The first gather pass is equivalent to rendering an opaque object.
+	// That is, only the front-most fragments are rendered.
+	outFragColor = inColor;
+}
+