// Copyright 2023 ZSttt, Inc. All Rights Reserved.

#include "/Engine/Public/Platform.ush"
#include "/Engine/Private/Common.ush"

#ifndef FLOWFIELD2D_USE_COMPUTE
	#define FLOWFIELD2D_USE_COMPUTE true
#endif

float2 QuadSize;
#if FLOWFIELD2D_USE_COMPUTE
StructuredBuffer<float2> Particles;
#else
Texture2D<float4> Particles;
uint2 ParticlesResolution;
#endif

void DrawParticles
(
	in float4 Vertex : ATTRIBUTE0,
	uint IId : SV_InstanceID,
	out float2 OutParticle : TEXCOORD0,
	out float4 Output : SV_POSITION
)
{
 #if FLOWFIELD2D_USE_COMPUTE
    OutParticle = Particles[IId];
 #else
    uint2 Pos = uint2(IId / ParticlesResolution.x, IId % ParticlesResolution.x);
    float4 color = Particles.Load(uint3(Pos, 0));
    OutParticle = float2(color.r / 255.0 + color.b, color.g / 255.0 + color.a);
#endif
    float2 UV = OutParticle.xy + (QuadSize * Vertex.xy);
    UV = 2.0 * UV - 1.0;
    Output = float4(UV.r, UV.g, 0.0, 1.0);
}