ethannicholas | f008b0a | 2016-09-30 06:23:24 -0700 | [diff] [blame] | 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. |