You can disable the attribute array by calling
Either way, since attributes cannot be used unless enabled, and are disabled by default, you need to call
enableVertexAttribArray() to enable individual attributes so that they can be used. Once that's been done, other methods can be used to access the attribute, including
GLuintspecifying the index number that uniquely identifies the vertex attribute to enable. If you know the name of the attribute but not its index, you can get the index by calling
To check for errors after calling
indexis invalid; that is, it's greater than or equal to the maximum number of entries permitted in the context's vertex attribute list, as indicated by the value of
This code — a snippet taken from the full example A basic 2D WebGL animation example — shows the use of
enableVertexArray() to activate the attribute that will be used by the WebGL layer to pass individual vertexes from the vertex buffer into the vertex shader function.
gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer); aVertexPosition = gl.getAttribLocation(shaderProgram, "aVertexPosition"); gl.enableVertexAttribArray(aVertexPosition); gl.vertexAttribPointer(aVertexPosition, vertexNumComponents, gl.FLOAT, false, 0, 0); gl.drawArrays(gl.TRIANGLES, 0, vertexCount);
animateScene()in "A basic 2D WebGL animation example." See that article for the full sample and to see the resulting animation in action.
This code sets the buffer of vertexes that will be used to draw the triangles of the shape by calling
bindBuffer(). Then the vertex position attribute's index is obtained from the shader program by calling
With the index of the vertex position attribute now available in
aVertexPosition, we call
enableVertexAttribArray() to enable the position attribute so it can be used by the shader program (in particular, by the vertex shader).
Then the vertex buffer is bound to the
aVertexPosition attribute by calling
vertexAttribPointer(). This step is not obvious, since this binding is almost a side effect. But as a result, accessing
aVertexPosition now obtains data from the vertex buffer.
With the association in place between the vertex buffer for our shape and the
aVertexPosition attribute used to deliver vertexes one by one into the vertex shader, we're ready to draw the shape by calling
|WebGL 1.0 |
The definition of 'enableVertexAttribArray' in that specification.
|OpenGL ES 2.0 |
The definition of 'glEnableVertexAttribArray' in that specification.
|Standard||Man page of the OpenGL API.|
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