
/**
 * 编译着色器程序
 * @param gl {WebGLRenderingContext} The current WebGL context {WebGLProgram}
 * @param vertexSrc  The vertex shader source as an array of strings.顶点着色器
 * @param fragmentSrc  The fragment shader source as an array of strings.片元着色器
 * @param attributeLocations {Object} An attribute location map that lets you manually set the attribute locations
 * @return {WebGLProgram} the shader program 返回着色器程序
 */
export function compileProgram(gl:WebGLRenderingContext, vertexSrc:string, fragmentSrc:string, attributeLocations?:any):WebGLProgram {
    var glVertShader = compileShader(gl, gl.VERTEX_SHADER, vertexSrc);
    var glFragShader = compileShader(gl, gl.FRAGMENT_SHADER, fragmentSrc);

    var program = gl.createProgram();

    gl.attachShader(program, glVertShader);
    gl.attachShader(program, glFragShader);

    // optionally, set the attributes manually for the program rather than letting WebGL decide..
    if (attributeLocations) {
        for (var i in attributeLocations) {
            gl.bindAttribLocation(program, attributeLocations[i], i);
        }
    }


    gl.linkProgram(program);

    // if linking fails, then log and cleanup
    if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
        console.error('Error: Could not initialize shader.');
        console.error('gl.VALIDATE_STATUS', gl.getProgramParameter(program, gl.VALIDATE_STATUS));
        console.error('gl.getError()', gl.getError());

        // if there is a program info log, log it
        if (gl.getProgramInfoLog(program) !== '') {
            console.warn('Warning: gl.getProgramInfoLog()', gl.getProgramInfoLog(program));
        }

        gl.deleteProgram(program);
        program = null;
    }

    // clean up some shaders
    gl.deleteShader(glVertShader);
    gl.deleteShader(glFragShader);

    return program;
};

/**
 * 创建shader
 * @private
 * @param gl {WebGLRenderingContext} The current WebGL context {WebGLProgram}
 * @param type {Number} the type, can be either VERTEX_SHADER or FRAGMENT_SHADER
 * @param vertexSrc {string|string[]} The vertex shader source as an array of strings.
 * @return {WebGLShader} the shader
 */
var compileShader = function (gl:WebGLRenderingContext, type:number, src:string):WebGLShader {
    var shader = gl.createShader(type);

    gl.shaderSource(shader, src);
    gl.compileShader(shader);

    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
        console.error(src);
        console.error(gl.getShaderInfoLog(shader));
        return null;
    }

    return shader;
};
