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This article shares with you the content of the sample analysis of Shader in Unity. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

Template Test Summary

To get to the point, stencil is similar to color buffers and depth buffers, which hold an unsigned integer value (usually an 8-bit integer) for each pixel on the screen. The specific meaning of this value depends on the specific application of the program. In the process of rendering, you can use this value to compare with a preset reference value, and decide whether to update the color value of the corresponding pixel according to the result of the comparison. This process of comparison is called template testing. Template testing occurs after the transparency test (alpha test) and before the in-depth test (depth test). If the template test passes, the corresponding pixel is updated, otherwise it is not updated. In the graphics rendering pipeline, the sequence of test operations based on a single pixel is as follows

Template test syntax

In general, the complete syntax format of stencil is as follows:

Stencil {Ref referenceValue ReadMask readMask WriteMask writeMask Comp comparisonFunction Pass stencilOperation Fail stencilOperation ZFail stencilOperation}

Ref

Ref referenceValue

Ref is used to set the reference value referenceValue, which will be used to compare with the value in the template buffer. ReferenceValue is an integer with values in the range of 0-255.

ReadMask

ReadMask readMask

The literal meaning of ReadMask is to read the mask. ReadMask will operate bitwise and (&) with referenceValue and stencilBufferValue. ReadMask values also range from 0 to 255. the default value is 255. the binary bit is 11111111, that is, it does not have an effect on referenceValue and stencilBufferValue when reading, but reads the original values.

WriteMask

WriteMask writeMask

WriteMask is masked when writing to the template buffer (bitwise and [&]). The value of writeMask ranges from 0 to 255. the default value is also 255. that is, when the stencilBufferValue value is modified, the original value is still written.

Comp

Comp comparisonFunction

Comp is an operation function that defines a comparison between the reference value (referenceValue) and the buffer value (stencilBufferValue). Default value: always

Pass

Pass stencilOperation

Pass defines that when the template test (and depth test) passes, the template buffer value (stencilBufferValue) is processed according to (stencilOperation value). Default value: keep

Fail

Fail stencilOperation

Fail defines that when the template test (and depth test) fails, the template buffer value (stencilBufferValue) is processed according to (stencilOperation value). Default value: keep

ZFail

ZFail defines that when the template test passes and the depth test fails, the template buffer value (stencilBufferValue) is processed according to (stencilOperation value). Default value: keep

Comp,Pass,Fail and ZFail will be applied to geometry that is hidden on the back (only the previous geometry is rendered), unless Cull Front is specified, in which case it is geometry that is hidden on the front (only geometry on the back is rendered). You can also precisely specify the double-sided template state by defining CompFront,PassFront,FailFront,ZFailFront (when the model is used for front-facing geometry) and ComBack,PassBack,FailBack,ZFailBack (when the model is used for back-facing geometry).

Judgment basis of template testing

Like depth testing, template testing for each pixel in unity has its own set of independent criteria, with the following formula:

If (referenceValue&readMask comparisonFunction stencilBufferValue&readMask)

Through pixel

Else

Discard pixels

In this formula, it is mainly divided into the left part and the right part of comparisonFunction

ReferenceValue is defined by Ref, which is defined by programmers. ReadMask is the template value read mask, which performs bitwise and (&) operations with referenceValue as the result on the left side of the formula. The default value is 255.The result of bitwise and (&) is referenceValue itself.

StencilBufferValue is the value of the current template buffer at the corresponding location, which is also masked and manipulated with readMask, and the result is the part on the right.

The comparisonFunction comparison operation is defined by the Comp command, by which the results on the left and right sides of the formula are judged, and their values and meanings are shown in the list below.

Greater is equivalent to ">" operation, that is, only if left > right, template test passes, render pixel GEqual is equivalent to "> =" operation, that is, only if left > = right, template test passes, render pixel Less equals "

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