RenderScript ScriptC中的gl_FragCoord等效项

Question

我正在将一些GLSL着色器移植到Renderscript中。

在Renderscript ScriptC中模拟gl_FragCoord的等效方式是什么？

GLSL着色器：

uniform sampler2D u_texture;
varying vec2 v_texcoord;
uniform vec2 resolution;

void main()
{
    vec4 color = texture2D(u_texture, v_texcoord);

    vec2 position = (gl_FragCoord.xy / resolution.xy) - vec2(0.5);
    float len = length(position);

    gl_FragColor = color * vec4(vec3(len), 1.0);
}

渲染脚本：

rs_allocation texture;
rs_sampler sampler;
float2 resolution;

uchar4 __attribute__((kernel)) root(uint32_t x, uint32_t y)
{
    float2 texcoord = (float2){(float)x, (float)y} * (float2){ 1.0f / resolution.x, 1.0f / resolution.y};
    float4 color = rsSample(texture, sampler, texcoord);

    -----------------------------------------------------------------
    float2 position = (***gl_FragCoord.xy*** / resolution.xy) - 0.5f;
    -----------------------------------------------------------------

    float len = length(position);
    color *= (float4){len, len, len, 1.0f}

    return rsPackColorTo8888(color);
}

Answer 1

您已经在代码中使用了它，输入的x和y参数等效于gl_FragCoord.xy ，还请注意，乘以resolution.xy的倒数与首先除以它是相同的：

float2 texcoord = (float2){(float)x, (float)y} / (float2){resolution.x, resolution.y};