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WebGLRenderingContext.isEnabled() - Web API 接口参考编辑

WebGLRenderingContext.isEnabled() 是 WebGL API 方法之一，用来检测给定的 WebGL 功能项在当前上下文是否可用。

默认的，除了 gl.DITHER，所有的功能项都是未启用的。

句法

void gl.isEnabled(cap);

参数

cap

GLenum 指定待检测的 WebGL 功能项。可能的值有：

Constant	Description
`gl.BLEND`	Blending of the computed fragment color values. See `WebGLRenderingContext.blendFunc()`.
`gl.CULL_FACE`	Culling of polygons. See `WebGLRenderingContext.cullFace()`.
`gl.DEPTH_TEST`	Depth comparisons and updates to the depth buffer. See `WebGLRenderingContext.depthFunc()`.
`gl.DITHER`	Dithering of color components before they get written to the color buffer.
`gl.POLYGON_OFFSET_FILL`	Adding an offset to depth values of polygon's fragments. See `WebGLRenderingContext.polygonOffset()`.
`gl.SAMPLE_ALPHA_TO_COVERAGE`	Computation of a temporary coverage value determined by the alpha value.
`gl.SAMPLE_COVERAGE`	ANDing the fragment's coverage with the temporary coverage value. See `WebGLRenderingContext.sampleCoverage()`.
`gl.SCISSOR_TEST`	Scissor test that discards fragments that are outside of the scissor rectangle. See `WebGLRenderingContext.scissor()`.
`gl.STENCIL_TEST`	Stencil testing and updates to the stencil buffer. See `WebGLRenderingContext.stencilFunc()`.

当使用 WebGL 2 context 的时候，下列附加的值也是可选用的。

Constant	Description
`gl.RASTERIZER_DISCARD`	Primitives are discarded immediately before the rasterization stage, but after the optional transform feedback stage. `gl.clear()` commands are ignored.

返回值

GLboolean 指示能力项 cap 可用 (true)，不可用 (false)。

示例

gl.isEnabled(gl.STENCIL_TEST);
// false

启用或停用给定的能力项，使用 WebGLRenderingContext.enable() 方法和 WebGLRenderingContext.disable() 方法：

gl.enable(gl.STENCIL_TEST);
gl.disable(gl.STENCIL_TEST);

规范

Specification	Status	Comment
WebGL 1.0 isEnabled	Recommendation	Initial definition for WebGL.
OpenGL ES 2.0 glIsEnabled	Standard	Man page of the (similar) OpenGL ES 2.0 API.
WebGL 2.0 isEnabled	Editor's Draft	Updated definition for WebGL 2.
OpenGL ES 3.0 glIsEnabled	Standard	Man page of the (similar) OpenGL ES 3.0 API.

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