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1 Overview | |
2 ======== | |
3 | |
4 SkSL ("Skia Shading Language") is a variant of GLSL which is used as Skia's | |
5 internal shading language. SkSL is, at its heart, a single standardized version | |
6 of GLSL which avoids all of the various version and dialect differences found | |
7 in GLSL "in the wild", but it does bring a few of its own changes to the table. | |
8 | |
9 Skia uses the SkSL compiler to convert SkSL code to GLSL, GLSL ES, or SPIR-V | |
10 before handing it over to the graphics driver. | |
11 | |
12 Differences from GLSL | |
13 ===================== | |
14 | |
15 SkSL is based on GLSL 4.5. For the most part, write SkSL exactly as you would | |
16 desktop GLSL, and the SkSL compiler will take care of version and dialect | |
17 differences (for instance, you always use "in" and "out", and skslc will handle | |
18 translating them to "varying" and "attribute" as appropriate). Be aware of the | |
19 following differences between SkSL and GLSL: | |
20 | |
21 * no #version or "precision" statement is required, and they will be ignored if | |
22 present | |
23 * the output color is sk_FragColor (do not declare it) | |
24 * lowp, mediump, and highp are always permitted (but will only be respected if | |
25 you run on a GLES device) | |
26 * you do not need to include ".0" to make a number a float (meaning that | |
27 "vec2(x, y) * 4" is perfectly legal in SkSL, unlike GLSL where it would often | |
28 have to be expressed "vec2(x, y) * 4.0". There is no performance penalty for | |
29 this, as the number is converted to a float at compile time) | |
30 * type suffixes on numbers (1.0f, 0xFFu) are both unnecessary and unsupported | |
31 * some built-in functions and one or two rarely-used language features are not | |
32 yet supported (sorry!) | |
33 | |
34 SkSL is still under development, and is expected to diverge further from GLSL | |
35 over time. | |
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