WebGL 2.0错误：glDrawArrays：尝试访问属性0中超出范围的顶点

Question

我正在学习WebGL技术。不幸的是我遇到了一些错误。我想为直升机绘制2D两种形状。我在下面编写了代码。我想做的就是将螺旋桨制作成称为主体的形状。

请注意，我尝试创建一个新缓冲区并将其绑定，但是仍然失败。我认为尚未了解跨步，但是即使它很简单，我也想学习如何解决。

// Vertex shader
var _vertexShader = `
    attribute vec4 _position;
    void main() {
        gl_Position = _position;
    }
`

// Fragment shader
var _fragmentShader = `
    precision mediump float;

    void main() {
        gl_FragColor = vec4(0.6, 0.8, 0.3, 1);
    }
`

// Create shader
function createShader(gl, type, source) {
    var shader = gl.createShader(type)
    gl.shaderSource(shader, source)
    gl.compileShader(shader)
    var success = gl.getShaderParameter(shader, gl.COMPILE_STATUS)
    if (success) {
        return shader
    } else {
        console.log(gl.getShaderInfoLog(shader))
        gl.deleteShader(shader)
        // return false
    }
}

// Linking shader by program
function createProgram(gl, vertexShader, fragmentShader) {
    var program = gl.createProgram()
    gl.attachShader(program, vertexShader)
    gl.attachShader(program, fragmentShader)
    gl.linkProgram(program)
    var success = gl.getProgramParameter(program, gl.LINK_STATUS)
    if (success) {
        return program
    } else {
        console.log(gl.getProgramInfoLog(program))
        gl.deleteProgram(program)
        // return false
    }
}

function main() {
    // Get a WebGL context.
    var canvas = document.getElementById('canvas')
    var gl = canvas.getContext('webgl2')
    if (!gl) {
        alert('Not support.')
        return false
    }

    // Get the strings for our GLSL shaders.
    var vertexShader = createShader(gl, gl.VERTEX_SHADER, _vertexShader)
    var fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, _fragmentShader)
    // Link the two shaders into a program.
    var program = createProgram(gl, vertexShader, fragmentShader)
    // Look up where the vertex data need to go.
    var positionLoc = gl.getAttribLocation(program, '_position')
    // Create a buffer and put the three 2d clip space points in it.
    var body_positionBuf = gl.createBuffer()
    // Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = body_positionBuf).
    gl.bindBuffer(gl.ARRAY_BUFFER, body_positionBuf)
    var body_positions = new Float32Array(
        [
            // Body triangle (Right)
            -0.25,  0,
            0.25,  0,
            0, 0.5,
            // Body triangle (Left) 
            -0.15, 0,
            0.15, 0,
            0.15, -0.25,
            // Body square
            -0.15, 0,
            -0.15, -0.25,
            0.15, -0.25,
        ]   
    )

    var roter_positions = new Float32Array([
        0.15, 0.1,
        0.15, -0.1,
        -0.15, 0.1,

        -0.15, -0.1,
        -0.15, 0.1,
        0.15, 0.1,
    ])

    gl.bufferData(gl.ARRAY_BUFFER, body_positions, gl.STATIC_DRAW)
    // Code above this line is initialization code.
    // Code below this line is rendering code.

    // webglUtils.resizeCanvasToDisplaySize(gl.canvas)
    // Tell WebGL how to convert from clip space to pixels.
    gl.viewport(0, 0, gl.canvas.width, gl.canvas.height)

    // Clear the canvas.
    gl.clearColor(0, 0, 0, 0)
    gl.clear(gl.COLOR_BUFFER_BIT)
    
    // Tell it to use our program (pair of shaders).
    gl.useProgram(program)
    // Turn on the attribute.
    gl.enableVertexAttribArray(positionLoc)
    // Bind the position buffer.
    gl.bindBuffer(gl.ARRAY_BUFFER, body_positionBuf)

    // Tell the attribute how to get data out of body_positionBuf (ARRAY_BUFFER).
    var size = 2
    var type = gl.FLOAT
    var normalize = false
    var stride = 0
    var offset = 0 
    gl.vertexAttribPointer(positionLoc, size, type, normalize, stride, offset)
    // Draw.
    var drawType = gl.TRIANGLES
    var count = body_positions.length / 2
    gl.drawArrays(drawType, offset, count)
}

main()

<canvas id="canvas" width="500" height="250"></canvas>

我该怎么办？我不知道。请帮助我。

Answer 1

在body_positions中指定的所有顶点坐标的拳头覆盖在roter_positions中指定的顶点。
更改顶点坐标：

var roter_positions = new Float32Array([
    0.15, 0.6,
    0.15, 0.4,
    -0.15, 0.6,

    -0.15, 0.4,
    -0.15, 0.6,
    0.15, 0.6,
])

请注意，我建议使用模型矩阵来分别定义每个对象的位置和方向。但是先解决您的问题，然后再进行下一步。

如果要使用2个缓冲区，则必须创建2个缓冲区对象，并且必须定义两个对象的数据存储：

var body_positionBuf = gl.createBuffer()
gl.bindBuffer(gl.ARRAY_BUFFER, body_positionBuf)
gl.bufferData(gl.ARRAY_BUFFER, body_positions, gl.STATIC_DRAW)

var roter_positionBuf = gl.createBuffer()
gl.bindBuffer(gl.ARRAY_BUFFER, roter_positionBuf)
gl.bufferData(gl.ARRAY_BUFFER, roter_positions, gl.STATIC_DRAW)  

最后，您可以通过2个单独的绘制调用在2个单独的缓冲区中绘制网格。您必须在每次绘制调用之前定义通用顶点属性数据的数组：

gl.bindBuffer(gl.ARRAY_BUFFER, body_positionBuf)
gl.vertexAttribPointer(positionLoc, 2, gl.FLOAT, false, 0, 0)       
gl.drawArrays(gl.TRIANGLES, 0, body_positions.length / 2)

gl.bindBuffer(gl.ARRAY_BUFFER, roter_positionBuf)
gl.vertexAttribPointer(positionLoc, 2, gl.FLOAT, false, 0, 0)       
gl.drawArrays(gl.TRIANGLES, 0, roter_positions.length / 2)

请参见示例，我将更改应用于您的原始代码：

// Vertex shader
var _vertexShader = `
    attribute vec4 _position;
    void main() {
        gl_Position = _position;
    }
`

// Fragment shader
var _fragmentShader = `
    precision mediump float;

    void main() {
        gl_FragColor = vec4(0.6, 0.8, 0.3, 1);
    }
`

// Create shader
function createShader(gl, type, source) {
    var shader = gl.createShader(type)
    gl.shaderSource(shader, source)
    gl.compileShader(shader)
    var success = gl.getShaderParameter(shader, gl.COMPILE_STATUS)
    if (success) {
        return shader
    } else {
        console.log(gl.getShaderInfoLog(shader))
        gl.deleteShader(shader)
        // return false
    }
}

// Linking shader by program
function createProgram(gl, vertexShader, fragmentShader) {
    var program = gl.createProgram()
    gl.attachShader(program, vertexShader)
    gl.attachShader(program, fragmentShader)
    gl.linkProgram(program)
    var success = gl.getProgramParameter(program, gl.LINK_STATUS)
    if (success) {
        return program
    } else {
        console.log(gl.getProgramInfoLog(program))
        gl.deleteProgram(program)
        // return false
    }
}

function main() {
    // Get a WebGL context.
    var canvas = document.getElementById('canvas')
    var gl = canvas.getContext('webgl2')
    if (!gl) {
        alert('Not support.')
        return false
    }

    // Get the strings for our GLSL shaders.
    var vertexShader = createShader(gl, gl.VERTEX_SHADER, _vertexShader)
    var fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, _fragmentShader)
    // Link the two shaders into a program.
    var program = createProgram(gl, vertexShader, fragmentShader)
    // Look up where the vertex data need to go.
    var positionLoc = gl.getAttribLocation(program, '_position')
    // Create a buffer and put the three 2d clip space points in it.
    
    var body_positions = new Float32Array(
        [
            // Body triangle (Right)
            -0.25,  0,
            0.25,  0,
            0, 0.5,
            // Body triangle (Left) 
            -0.15, 0,
            0.15, 0,
            0.15, -0.25,
            // Body square
            -0.15, 0,
            -0.15, -0.25,
            0.15, -0.25,
        ]   
    )

    var roter_positions = new Float32Array([
        0.15, 0.6,
        0.15, 0.4,
        -0.15, 0.6,

        -0.15, 0.4,
        -0.15, 0.6,
        0.15, 0.6,
    ])

    var body_positionBuf = gl.createBuffer()
    gl.bindBuffer(gl.ARRAY_BUFFER, body_positionBuf)
    gl.bufferData(gl.ARRAY_BUFFER, body_positions, gl.STATIC_DRAW)

    var roter_positionBuf = gl.createBuffer()
    gl.bindBuffer(gl.ARRAY_BUFFER, roter_positionBuf)
    gl.bufferData(gl.ARRAY_BUFFER, roter_positions, gl.STATIC_DRAW)
    
    // webglUtils.resizeCanvasToDisplaySize(gl.canvas)
    // Tell WebGL how to convert from clip space to pixels.
    gl.viewport(0, 0, gl.canvas.width, gl.canvas.height)

    // Clear the canvas.
    gl.clearColor(0, 0, 0, 0)
    gl.clear(gl.COLOR_BUFFER_BIT)
    
    // Tell it to use our program (pair of shaders).
    gl.useProgram(program)
    // Turn on the attribute.
    gl.enableVertexAttribArray(positionLoc)
    // Bind the position buffer.
    
    gl.bindBuffer(gl.ARRAY_BUFFER, body_positionBuf)
    gl.vertexAttribPointer(positionLoc, 2, gl.FLOAT, false, 0, 0)       
    gl.drawArrays(gl.TRIANGLES, 0, body_positions.length / 2)

    gl.bindBuffer(gl.ARRAY_BUFFER, roter_positionBuf)
    gl.vertexAttribPointer(positionLoc, 2, gl.FLOAT, false, 0, 0)       
    gl.drawArrays(gl.TRIANGLES, 0, roter_positions.length / 2)
}

main();

<canvas id="canvas" width="500" height="250"></canvas>

---

当然，您可以将2个数组添加到1个缓冲区中。您必须使用数据存储创建一个缓冲区，该缓冲区对于两个阵列都足够大。通过gl.bufferData将数据添加到缓冲区：

var body_bytes = body_positions.length * 4;
var roter_bytes = roter_positions.length * 4;

var common_positionBuf = gl.createBuffer()
gl.bindBuffer(gl.ARRAY_BUFFER, common_positionBuf)
gl.bufferData(gl.ARRAY_BUFFER, body_bytes + roter_bytes, gl.STATIC_DRAW); 
gl.bufferSubData(gl.ARRAY_BUFFER, 0, body_positions);
gl.bufferSubData(gl.ARRAY_BUFFER, body_bytes, roter_positions);

可以通过singel绘制调用来绘制网格：

gl.bindBuffer(gl.ARRAY_BUFFER, common_positionBuf)
gl.vertexAttribPointer(positionLoc, 2, gl.FLOAT, false, 0, 0) 
var no_of_vertices = (body_positions.length + roter_positions.length) / 2      
gl.drawArrays(gl.TRIANGLES, 0, no_of_vertices)

如果必须更改某些程序资源，则在绘制第二个网格之前（例如，模型矩阵均匀），也可以通过两个绘制调用来完成：

gl.drawArrays(gl.TRIANGLES, 0, body_positions.length / 2)

// change resources here ...

gl.drawArrays(gl.TRIANGLES, body_positions.length / 2, roter_positions.length / 2)

根据问题的原始代码，查看示例：

// Vertex shader
var _vertexShader = `
    attribute vec4 _position;
    void main() {
        gl_Position = _position;
    }
`

// Fragment shader
var _fragmentShader = `
    precision mediump float;

    void main() {
        gl_FragColor = vec4(0.6, 0.8, 0.3, 1);
    }
`

// Create shader
function createShader(gl, type, source) {
    var shader = gl.createShader(type)
    gl.shaderSource(shader, source)
    gl.compileShader(shader)
    var success = gl.getShaderParameter(shader, gl.COMPILE_STATUS)
    if (success) {
        return shader
    } else {
        console.log(gl.getShaderInfoLog(shader))
        gl.deleteShader(shader)
        // return false
    }
}

// Linking shader by program
function createProgram(gl, vertexShader, fragmentShader) {
    var program = gl.createProgram()
    gl.attachShader(program, vertexShader)
    gl.attachShader(program, fragmentShader)
    gl.linkProgram(program)
    var success = gl.getProgramParameter(program, gl.LINK_STATUS)
    if (success) {
        return program
    } else {
        console.log(gl.getProgramInfoLog(program))
        gl.deleteProgram(program)
        // return false
    }
}

function main() {
    // Get a WebGL context.
    var canvas = document.getElementById('canvas')
    var gl = canvas.getContext('webgl2')
    if (!gl) {
        alert('Not support.')
        return false
    }

    // Get the strings for our GLSL shaders.
    var vertexShader = createShader(gl, gl.VERTEX_SHADER, _vertexShader)
    var fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, _fragmentShader)
    // Link the two shaders into a program.
    var program = createProgram(gl, vertexShader, fragmentShader)
    // Look up where the vertex data need to go.
    var positionLoc = gl.getAttribLocation(program, '_position')
    // Create a buffer and put the three 2d clip space points in it.
    
    var body_positions = new Float32Array(
        [
            // Body triangle (Right)
            -0.25,  0,
            0.25,  0,
            0, 0.5,
            // Body triangle (Left) 
            -0.15, 0,
            0.15, 0,
            0.15, -0.25,
            // Body square
            -0.15, 0,
            -0.15, -0.25,
            0.15, -0.25,
        ]   
    )

    var roter_positions = new Float32Array([
        0.15, 0.6,
        0.15, 0.4,
        -0.15, 0.6,

        -0.15, 0.4,
        -0.15, 0.6,
        0.15, 0.6,
    ])

    var body_bytes = body_positions.length * 4;
    var roter_bytes = roter_positions.length * 4;

    var common_positionBuf = gl.createBuffer()
    gl.bindBuffer(gl.ARRAY_BUFFER, common_positionBuf)
    gl.bufferData(gl.ARRAY_BUFFER, body_bytes + roter_bytes, gl.STATIC_DRAW); 
    gl.bufferSubData(gl.ARRAY_BUFFER, 0, body_positions);
    gl.bufferSubData(gl.ARRAY_BUFFER, body_bytes, roter_positions);

    // webglUtils.resizeCanvasToDisplaySize(gl.canvas)
    // Tell WebGL how to convert from clip space to pixels.
    gl.viewport(0, 0, gl.canvas.width, gl.canvas.height)

    // Clear the canvas.
    gl.clearColor(0, 0, 0, 0)
    gl.clear(gl.COLOR_BUFFER_BIT)
    
    // Tell it to use our program (pair of shaders).
    gl.useProgram(program)
    // Turn on the attribute.
    gl.enableVertexAttribArray(positionLoc)
    // Bind the position buffer.
    
    gl.bindBuffer(gl.ARRAY_BUFFER, common_positionBuf)
    gl.vertexAttribPointer(positionLoc, 2, gl.FLOAT, false, 0, 0) 
    var no_of_vertices = (body_positions.length + roter_positions.length) / 2      
    gl.drawArrays(gl.TRIANGLES, 0, no_of_vertices)
}

main();

<canvas id="canvas" width="500" height="250"></canvas>