Shaders_Step4.metal

Shaders_Step4.metal

// Shaders.metal
#include <metal_stdlib>
using namespace metal;

struct VertexOut {
    float4 position [[position]];
    float2 texCoords;
};

vertex VertexOut circle_vertex(uint vertexID [[vertex_id]]) {
    float2 positions[4] = {
        float2(-1.0, -1.0), float2(1.0, -1.0),
        float2(-1.0,  1.0), float2(1.0,  1.0)
    };

    VertexOut out;
    out.position = float4(positions[vertexID], 0.0, 1.0);
    out.texCoords = float2((positions[vertexID].x + 1.0) / 2.0, (1.0 - positions[vertexID].y) / 2.0);
    return out;
}

fragment half4 circle_fragment(VertexOut in [[stage_in]], constant float &time [[buffer(0)]]) {
    float2 center = float2(
        0.5 + 0.2 * sin(time * 0.8),
        0.5 + 0.2 * cos(time * 0.8)
    );

    float dist = distance(in.texCoords, center);
    float maxDist = 0.25;
    float influence = 1.0 - min(dist / maxDist, 1.0);
    influence = pow(max(influence, 0.0), 2.0);

    half4 circleColor = half4(1.0, 0.5, 0.2, 1.0);
    half4 backgroundColor = half4(0.1, 0.1, 0.1, 1.0);
    half4 finalColor = mix(backgroundColor, circleColor, influence);

    return finalColor;
}