#version 450
/* Copyright (c) 2023, 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(set = 0, binding = 0) uniform SceneConstants
{
	mat4  projection;
	mat4  view;
	float background_grayscale;
	uint  sortFragments;
	uint  fragmentMaxCount;
	uint  sortedFragmentCount;
} sceneConstants;

layout(set = 0, binding = 2, r32ui) uniform uimage2D linkedListHeadTex;

layout(set = 0, binding = 3) buffer FragmentBuffer {
	uvec3 data[];
} fragmentBuffer;

layout(set = 0, binding = 4) buffer FragmentCounter {
	uint value;
} fragmentCounter;

////////////////////////////////////////

void main()
{
	// Get the next fragment index
	const uint nextFragmentIndex = atomicAdd(fragmentCounter.value, 1U);

	// Ignore the fragment if the fragment buffer is full
	if(nextFragmentIndex >= sceneConstants.fragmentMaxCount)
	{
		discard;
	}

	// Update the linked list head
	const uint previousFragmentIndex = imageAtomicExchange(linkedListHeadTex, ivec2(gl_FragCoord.xy), nextFragmentIndex);

	// Add the fragment to the buffer
	fragmentBuffer.data[nextFragmentIndex] = uvec3(previousFragmentIndex, packUnorm4x8(inColor), floatBitsToUint(gl_FragCoord.z));
}