Add EXT_shader_texture_lod extension.

Another shader-only extension, with no API changes.

This contribution is funded by https://higharc.com/

README.md

@@ -220,6 +220,7 @@ Only the following for now:
 * [`WEBGL_draw_buffers`](https://www.khronos.org/registry/webgl/extensions/WEBGL_draw_buffers/)
 * [`EXT_blend_minmax`](https://www.khronos.org/registry/webgl/extensions/EXT_blend_minmax/)
 * [`EXT_texture_filter_anisotropic`](https://www.khronos.org/registry/webgl/extensions/EXT_texture_filter_anisotropic/)
+* [`EXT_shader_texture_lod`](https://www.khronos.org/registry/webgl/extensions/EXT_shader_texture_lod/)
 
 ### How can I keep up to date with what has changed in headless-gl?
 

src/javascript/extensions/ext-shader-texture-lod.js

@@ -0,0 +1,14 @@
+class EXTShaderTextureLod {}
+
+function getEXTShaderTextureLod (context) {
+  let result = null
+  const exts = context.getSupportedExtensions()
+
+  if (exts && exts.indexOf('EXT_shader_texture_lod') >= 0) {
+    result = new EXTShaderTextureLod()
+  }
+
+  return result
+}
+
+module.exports = { getEXTShaderTextureLod, EXTShaderTextureLod }

src/javascript/webgl-rendering-context.js

@@ -12,6 +12,7 @@ const { getSTACKGLResizeDrawingBuffer } = require('./extensions/stackgl-resize-d
 const { getWebGLDrawBuffers } = require('./extensions/webgl-draw-buffers')
 const { getEXTBlendMinMax } = require('./extensions/ext-blend-minmax')
 const { getEXTTextureFilterAnisotropic } = require('./extensions/ext-texture-filter-anisotropic')
+const { getEXTShaderTextureLod } = require('./extensions/ext-shader-texture-lod')
 const { getOESVertexArrayObject } = require('./extensions/oes-vertex-array-object')
 const {
   bindPublics,
@@ -65,7 +66,8 @@ const availableExtensions = {
   stackgl_resize_drawingbuffer: getSTACKGLResizeDrawingBuffer,
   webgl_draw_buffers: getWebGLDrawBuffers,
   ext_blend_minmax: getEXTBlendMinMax,
-  ext_texture_filter_anisotropic: getEXTTextureFilterAnisotropic
+  ext_texture_filter_anisotropic: getEXTTextureFilterAnisotropic,
+  ext_shader_texture_lod: getEXTShaderTextureLod
 }
 
 const privateMethods = [
@@ -1227,6 +1229,10 @@ class WebGLRenderingContext extends NativeWebGLRenderingContext {
       exts.push('OES_vertex_array_object')
     }
 
+    if (supportedExts.indexOf('GL_EXT_shader_texture_lod') >= 0) {
+      exts.push('EXT_shader_texture_lod')
+    }
+
     return exts
   }