glsl - 我如何标准化在 glsl 中绘制的圆，这样分辨率就不会拉伸(stretch)？

Question

我正在尝试使用 glsl 围绕特定 Sprite 创建一个圆圈。然而，分辨率是矩形 (800x600)，这会导致一个略微拉伸(stretch)的圆圈:

我试过答案here ，但我不知道如何将它们正确应用到我的特定着色器。我需要做什么

#define SHADER_NAME SPOTLIGHT_FS
precision highp float;

uniform sampler2D uMainSampler;
varying vec2 outTexCoord;
// coord is the non-normalized position if the sprite that the circle follows
uniform vec2 coord;
vec2 px = vec2(1.0/800.0, 1.0/600.0);

float getDistance(vec2 pixelCoord, vec2 playerCoord) {
    // pixelCoord is normalized, but playerCoord is passed in as-is
    return distance(pixelCoord, playerCoord*px);
}

void main( void )
{
    if (getDistance(outTexCoord, coord) > 0.125) {
        gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0);
    }
    else {
        gl_FragColor = texture2D(uMainSampler, outTexCoord);
    }
}

Answer 1

您必须考虑视口(viewport)的纵横比。例如:

vec2 px = vec2(1.0/800.0, 1.0/600.0);
float aspect = 800.0 / 600.0; 

float getDistance(vec2 pixelCoord, vec2 playerCoord) {
    vec2 p = playerCoord * px * vec2(1.0, 1.0/aspect);
    // pixelCoord is normalized, but playerCoord is passed in as-is
    return distance(pixelCoord, p);
}

或者，您可以以像素为单位计算距离:

vec2 resolution = vec2(800.0, 600.0);
float radius = 100.0; // radius in pixel

float getDistance(vec2 pixelCoord, vec2 playerCoord) {
    return distance(pixelCoord*resolution, playerCoord);
}

void main( void )
{
    if (getDistance(outTexCoord, coord) > radius) {
        gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0);
    }
    else {
        gl_FragColor = texture2D(uMainSampler, outTexCoord);
    }
}