1

I have a vertex buffer containing several (in this case 2) graphs in the following structure:

var vertices = [ 
  x0, y00, y10,
  x1, y01, y11,
  x2, y02, y12,
  ...
  xn, y0n, y1n
];

and its indices

var indices = [0, 1, 2, 3, ... n-1];

You can notice that for each x value there is 2 y values each determining the graph.

What I want is to render those 2 graphs using this single buffer without any duplication of the x values.

Currently in the render loop I have this:

    function render() {         
        gl.bindBuffer(gl.ARRAY_BUFFER, vBuff);  // bind our buffer                                                      

        // with this setup it renders only first graph:
        // x0, y00,  
        // x1, y01, 
        // x2, y02, 
        // ... 
        // xn, y0n
        gl.vertexAttribPointer(vertexPositionLocation, 2, gl.FLOAT, false, 4*3, 0);     
        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);                                            
        gl.drawElements(gl.LINE_STRIP, indices.length, gl.UNSIGNED_SHORT, 0);

        // now how do I set up the vertexAttribPointer such that next draw call here 
        // would render second graph containing these points
        // x0, y10,  
        // x1, y11, 
        // x2, y12, 
        // ... 
        // xn, y1n      
        // ?
    }
4

1 回答 1

2

如果您严格希望通过属性指针来执行此操作，您可以将您的位置拆分为两个引用同一缓冲区的属性：

    // first call
    gl.vertexAttribPointer(vertexPositionXLocation, 1, gl.FLOAT, false, 4*3, 0);
    gl.vertexAttribPointer(vertexPositionYLocation, 1, gl.FLOAT, false, 4*3, 4);
    gl.drawArrays(gl.LINE_STRIP, 0, numDataPoints);

    // second call
    gl.vertexAttribPointer(vertexPositionYLocation, 1, gl.FLOAT, false, 4*3, 8);
    gl.drawArrays(gl.LINE_STRIP, 0, numDataPoints);

你的顶点着色器看起来像这样：

attribute float vX;
attribute float vY;
void main () { gl_Position=vec4(vX,vY,0,1); }

另请注意，我使用drawArrays而不是drawElements因为您暗示无论如何您都有线性索引缓冲区。

于 2019-03-19T23:56:01.067 回答