// glow.fsh
#ifdef GL_ES
precision mediump float;
#endif

varying vec4 v_fragmentColor;
varying vec2 v_texCoord;

uniform vec2 resolution; // 纹理大小（宽和高）范围是0~1
uniform vec3 glow_color;    // 发光颜色
uniform float glow_expand; // 发光强度
uniform float glow_range;  // 发光范围

const float sampleNum = 5;
const float AsNotAlpha = 0.3;  // 0.0 - 1.0
// 思路：先过滤不透明点，然后按照角度找到这个范围内不透明的点的“不透明程度”，不透明程度越高，发光越多

void debug(float x)
{
    //vec4 col = texture2D(CC_Texture0, v_texCoord.xy);
    // if (v_texCoord.x > 0.5 && v_texCoord.y > 0.5) 
    {
        gl_FragColor = vec4(x/255.0, x/255.0, x/255.0, 1.1);
    }
}

// 获取像素周围不透明点的数量
int getStrokeCount()
{
    vec2 unit = 1.0 / resolution.xy;//单位坐标
    float r = glow_range;
    float step = r / sampleNum;
    int count = 0;
    //遍历一个矩形，当前的坐标为中心点，遍历矩形中每个像素点的颜色
    for(float x = -r; x < r; x += step)
    {
        for(float y = -r; y < r; y += step)
        {
            vec4 col = texture2D(CC_Texture0, v_texCoord + vec2(x * unit.x, y * unit.y));
            if(col.a > AsNotAlpha)
            {
                count = count + 1;
            }
        }
    }
    return count;
}

void main()
{
    vec4 myC = texture2D(CC_Texture0, v_texCoord);
    
    if (myC.a > AsNotAlpha)
    {
        gl_FragColor = v_fragmentColor * myC;
        return;
    }

    // 获取像素周围不透明点的数量
    int strokeCount = getStrokeCount();
    
    float totalSample = (sampleNum * sampleNum * 2);
    float limit = totalSample * 0.8;
    if (strokeCount > limit)  //四周围至少有一个点是不透明的，这个点要设成描边颜色
    {
        myC.rgb = glow_color * glow_expand;
        myC.a = (strokeCount ) * glow_expand / totalSample;
    }
    else
    {
        myC.rgb = glow_color * strokeCount * glow_expand / limit;
        myC.a = (strokeCount ) * glow_expand / totalSample;
    }

    gl_FragColor = v_fragmentColor * myC;
}