Optional stencil描述模板测试的方法。默认ALWAYS，总是通过。
A GLenum specifying the test function. The default function is gl.ALWAYS.
Optional stencil模板测试时使用的mask值，默认全为1（0xFFFFFFFF）。
A GLuint specifying a bit-wise mask that is used to AND the reference value and the stored stencil value when the test is done. The default value is all 1.
Optional stencil一个为模板测试指定参考值。这个值被限制在0到2^n -1的范围内，其中n是模板缓冲区中的位数。默认0。
A GLint specifying the reference value for the stencil test. This value is clamped to the range 0 to 2^n -1 where n is the number of bitplanes in the stencil buffer. The default value is 0.
Optional stencil指定位掩码以启用或禁用在模板平面中写入单个位的正整数。默认全为1（0xFFFFFFFF）。
A GLuint specifying a bit mask to enable or disable writing of individual bits in the stencil planes. By default, the mask is all 1.
Optional stencil指定模板测试失败时使用的函数的枚举。默认KEEP，保持当前值。
A GLenum specifying the function to use when the stencil test fails. The default value is gl.KEEP.
Optional stencil指定在模板测试通过但深度测试失败时使用的函数枚举。默认KEEP，保持当前值。
A GLenum specifying the function to use when the stencil test passes, but the depth test fails. The default value is gl.KEEP.
Optional stencil指定在模板测试和深度测试通过时使用的函数枚举，或在模板测试通过且没有深度缓冲或禁用深度测试时使用的函数枚举。默认KEEP，保持当前值。
A GLenum specifying the function to use when both the stencil test and the depth test pass, or when the stencil test passes and there is no depth buffer or depth testing is disabled. The default value is gl.KEEP.
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模板单面状态。定义如何比较与运算模板值。