The ANGLE_instanced_arrays extension is part of the WebGL API and allows to draw the same object, or groups of similar objects multiple times, if they share the same vertex data, primitive count and type.
WebGL extensions are available using the WebGLRenderingContext.getExtension() method. For more information, see also Using Extensions in the WebGL tutorial.
Note: This extension is only available to WebGL1 contexts. In WebGL2, the functionality of this extension is available on the WebGL2 context by default and the constants and methods are available without the "ANGLE" suffix.
Despite the name "ANGLE", this extension works on any device if the hardware supports it and not just on Windows when using the ANGLE library. "ANGLE" just indicates that this extension has been written by the ANGLE library authors.
This extension exposes one new constant, which can be used in the gl.getVertexAttrib() method:
ext.VERTEX_ATTRIB_ARRAY_DIVISOR_ANGLE-
Returns a GLint describing the frequency divisor used for instanced rendering when used in the gl.getVertexAttrib() as the pname parameter.
This extension exposes three new methods.
ext.drawArraysInstancedANGLE()-
Behaves identically to gl.drawArrays() except that multiple instances of the range of elements are executed, and the instance advances for each iteration.
ext.drawElementsInstancedANGLE()-
Behaves identically to gl.drawElements() except that multiple instances of the set of elements are executed and the instance advances between each set.
ext.vertexAttribDivisorANGLE()-
Modifies the rate at which generic vertex attributes advance when rendering multiple instances of primitives with ext.drawArraysInstancedANGLE() and ext.drawElementsInstancedANGLE().
The following example shows how to draw a given geometry multiple times with a single draw call.
Warning: The following is educational, not production level code. It should generally be avoided to construct data / buffers within the rendering loop or right before use.
const ext = gl.getExtension("ANGLE_instanced_arrays");
gl.bindBuffer(gl.ARRAY_BUFFER, geometryVertexBuffer);
gl.enableVertexAttribArray(vertexPositionAttributeLocation);
gl.vertexAttribPointer(
vertexPositionAttributeLocation,
3,
gl.FLOAT,
false,
0,
0,
);
const instancePositions = [];
for (const instance of instances) {
instancePositions.push(
instance.position.x,
instance.position.y,
instance.position.z,
);
}
const instancePositionBuffer = createWebGLBufferFromData(instancePositions);
gl.bindBuffer(gl.ARRAY_BUFFER, instancePositionBuffer);
gl.enableVertexAttribArray(instancePositionAttributeLocation);
gl.vertexAttribPointer(
instancePositionAttributeLocation,
3,
gl.FLOAT,
false,
0,
0,
);
ext.vertexAttribDivisorANGLE(instancePositionAttributeLocation, 1);
ext.drawArraysInstancedANGLE(
gl.TRIANGLES,
0,
numGeometryVertices,
instances.length,
);