vertexAttribPointer的目的是什么？

Question

我正在使用javascript和webgl编写游戏引擎.为了测试它,我编写了一个绘制立方体的程序.要使这个程序工作,必须在调用绑定缓冲区之后但在调用绘制三角形之前调用vertexAttribPointer.我想知道这个方法到底是做什么的,为什么我必须按此顺序调用这些方法？

我最好的猜测是它初始化属性,但我不明白为什么必须在客户端调用它,如果是这种情况.

我在下面列出了一些来源.一切都是用打字稿写的.有关完整资料,请参阅github.com/dkellycollins/nemesis

设置着色器:

var cubeShader = new shaderProgram();
cubeShader.addShader(shaders.colorVertexShader);
cubeShader.addShader(shaders.colorFragmentShader);
cubeShader.init();
cubeShader.enableAttrib("position", 3, 4 * (3 + 3), 0);
cubeShader.enableAttrib("color", 3, 4 * (3 + 3), 3 * 4);

ShaderProgram:

class shaderProgram {
    constructor() {
        this.Id = gl.createProgram();
    }

    public Id;

    public addShader(shader:WebGLShader[]):void {
        if(shader instanceof Array) {
            shader.forEach(s => {
                gl.attachShader(this.Id, s);
            });
        } else {
            gl.attachShader(this.Id, shader);
        }
    }

    public init():void {
        gl.linkProgram(this.Id);
    }

    public setActive() {
        gl.useProgram(this.Id);
    }

    public enableAttrib(attribName: string, index: number, stride:number, offset: number) {
        var attrib = gl.getAttribLocation(this.Id, attribName);
        gl.enableVertexAttribArray(attrib);
        gl.vertexAttribPointer(attrib, index, gl.FLOAT, false, stride, offset);
    }

    public setFloatAttrib(attribName:string, value:number) {
        var attrib = gl.getAttribLocation(this.Id, attribName);
        gl.vertexAttrib1f(attrib, value);
    }

    public setMatrix(uniName: string, value: number[]) {
        var uniform = gl.getUniformLocation(this.Id, uniName);
        gl.uniformMatrix4fv(uniform, false, value);
    }
}

渲染立方体:

public render():void {
    gl.drawElements(gl.TRIANGLES, this._triangles, gl.UNSIGNED_SHORT, 0);
}

顶点着色器源:

attribute vec3 position; //the position of the point
uniform mat4 Pmatrix;
uniform mat4 Vmatrix;
uniform mat4 Mmatrix;
attribute vec3 color; //the color of the point
varying vec3 vColor;
void main(void) { //pre-built function
    gl_Position = Pmatrix*Vmatrix*Mmatrix*vec4(position, 1.); //0. is the z, and 1 is w
    vColor=color;
}

Answer 1

它告诉WebgL如何解释数据:

gl.vertexAttribPointer(attrib, index, gl.FLOAT, false, stride, offset);

这意味着:对于属性,attrib有一些index类型的组件,从当前绑定的开始和分开开始gl.FLOAT进行not标准化.offsetstridegl.ARRAY_BUFFER

只要可以如上所述,客户端可以随意设置其数据.