常用的OpenGL滤镜

以下滤镜在OpenGL ES 2.0版本运行，用OES纹理对相机预览图像处理。

四分镜

#extension GL_OES_EGL_image_external : require
precision mediump float;

varying vec2 textureCoordinate;
uniform samplerExternalOES vTexture;

void main() {
    vec2 uv = textureCoordinate;
    if (uv.x <= 0.5) {
        uv.x = uv.x * 2.0;
    } else {
        uv.x = (uv.x - 0.5) * 2.0;
    }

    if (uv.y <= 0.5) {
        uv.y = uv.y * 2.0;
    } else {
        uv.y = (uv.y - 0.5) * 2.0;
    }
    gl_FragColor = texture2D(vTexture, uv);
}