CODEWITHSUNDEEP
openglglslshaderrgbyuv
lee
lee

Reputation: 29

RGB to YUV using shader

I want to use fragment shader to convert RGB to YUV420P using shader.

1，I figured out the coordinates of the current texture color.

2，I calculated the 4 Y and put it on the current color.

My code:

    precision mediump float;
    varying vec2 vTextureCoord;
    uniform sampler2D tex;
    uniform float width;
    uniform float height;
    uniform float offset;
    uniform vec3 scal;

    void main(void) {
        vec2 nowTxtPos = vTextureCoord;
        vec2 size = vec2(width, height);
    // y
        if(nowTxtPos.y<0.25){
    // y1 postion
            vec2 now_pos = nowTxtPos * size;
            vec2 basePos = now_pos * vec2(4.0,4.0);
            float addY = float(int(basePos.x / width));
            basePos.x = basePos.x - addY * width;
            basePos.y += addY;

            float y1,y2,y3,y4;
            vec2 samplingPos = basePos / size;
            vec4 texel = texture2D(tex, samplingPos);
            y1 = dot(texel.rgb, scal);
            y1 += offset;

            basePos.x+=1.0;
            samplingPos = basePos/size;
            texel = texture2D(tex, samplingPos);
            y2 = dot(texel.rgb, scal);
            y2 += offset;

            basePos.x+=1.0;
            samplingPos = basePos/size;
            texel = texture2D(tex, samplingPos);
            y3 = dot(texel.rgb, scal);
            y3 += offset;

            basePos.x+=1.0;
            samplingPos = basePos/size;
            texel = texture2D(tex, samplingPos);
            y4 = dot(texel.rgb, scal);
            y4 += offset;

            gl_FragColor = vec4(y1, y2, y3, y4);
        }
    }

The picture(YUV420P):

picture

Enlarged post picture

It has aliasing. I don't know why.

Upvotes: 1

Views: 2709

Answers (1)

lee
lee

Reputation: 29

I have solved it. Because the calculation accuracy is not enough.

Edit here:

"precision mediump float;" -> "precision highp float;"

Upvotes: 1

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