webgl复习笔记——绘制三角形、四边形

代码结构基本不变，改drawArrays参数:gl.TRIANGLES

 webgl.drawArrays(webgl.TRIANGLES, 0, n);

function initBuffer() {
    let gl = webgl;
    let vertexs = new Float32Array(
        [.5, .5, .5, -.5, -.5, -.5,
            -.5,.5,-.7,.7,.7,.7]
    );
    let n = vertexs.length / 2;
    let buffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
    gl.bufferData(gl.ARRAY_BUFFER, vertexs, gl.STATIC_DRAW);
    let a_position = gl.getAttribLocation(gl.program, 'a_position');
    gl.vertexAttribPointer(a_position, 2, gl.FLOAT, false, 0, 0);
    gl.enableVertexAttribArray(a_position);
    return n;
}