support WEBGL_provoking_vertex

src/mol-gl/webgl/compat.ts

 /**
- * Copyright (c) 2018-2022 mol* contributors, licensed under MIT, See LICENSE file for more info.
+ * Copyright (c) 2018-2023 mol* contributors, licensed under MIT, See LICENSE file for more info.
  *
  * @author Alexander Rose <alexander.rose@weirdbyte.de>
  */
@@ -523,6 +523,31 @@ export function getFboRenderMipmap(gl: GLRenderingContext): COMPAT_fboRenderMipm
     return isWebGL2(gl) ? {} : gl.getExtension('OES_fbo_render_mipmap');
 }
 
+/**
+ * See https://registry.khronos.org/webgl/extensions/WEBGL_provoking_vertex/
+ */
+export interface COMPAT_provoking_vertex {
+    readonly FIRST_VERTEX_CONVENTION: number;
+    readonly LAST_VERTEX_CONVENTION: number;
+    readonly PROVOKING_VERTEX: number;
+    provokingVertex(provokeMode: number): void;
+}
+
+export function getProvokingVertex(gl: GLRenderingContext): COMPAT_provoking_vertex | null {
+    if (isWebGL2(gl)) {
+        const ext = gl.getExtension('WEBGL_provoking_vertex');
+        if (ext) {
+            return {
+                FIRST_VERTEX_CONVENTION: ext.FIRST_VERTEX_CONVENTION_WEBGL,
+                LAST_VERTEX_CONVENTION: ext.LAST_VERTEX_CONVENTION_WEBGL,
+                PROVOKING_VERTEX: ext.PROVOKING_VERTEX_WEBGL,
+                provokingVertex: ext.provokingVertexWEBGL.bind(gl)
+            };
+        }
+    }
+    return null;
+}
+
 export function getNoNonInstancedActiveAttribs(gl: GLRenderingContext): boolean {
     if (!isWebGL2(gl)) return false;
 

src/mol-gl/webgl/context.ts

@@ -239,6 +239,11 @@ export function createContext(gl: GLRenderingContext, props: Partial<{ pixelScal
         throw new Error('Need "MAX_VERTEX_TEXTURE_IMAGE_UNITS" >= 8');
     }
 
+    // optimize assuming flats first and last data are same or differences don't matter
+    // extension is only available when `FIRST_VERTEX_CONVENTION` is more efficient
+    const epv = extensions.provokingVertex;
+    epv?.provokingVertex(epv.FIRST_VERTEX_CONVENTION);
+
     let isContextLost = false;
     const contextRestored = new BehaviorSubject<now.Timestamp>(0 as now.Timestamp);
 

src/mol-gl/webgl/extensions.ts

 /**
- * Copyright (c) 2018-2022 mol* contributors, licensed under MIT, See LICENSE file for more info.
+ * Copyright (c) 2018-2023 mol* contributors, licensed under MIT, See LICENSE file for more info.
  *
  * @author Alexander Rose <alexander.rose@weirdbyte.de>
  */
 
-import { GLRenderingContext, COMPAT_instanced_arrays, COMPAT_standard_derivatives, COMPAT_vertex_array_object, getInstancedArrays, getStandardDerivatives, COMPAT_element_index_uint, getElementIndexUint, COMPAT_texture_float, getTextureFloat, COMPAT_texture_float_linear, getTextureFloatLinear, COMPAT_blend_minmax, getBlendMinMax, getFragDepth, COMPAT_frag_depth, COMPAT_color_buffer_float, getColorBufferFloat, COMPAT_draw_buffers, getDrawBuffers, getShaderTextureLod, COMPAT_shader_texture_lod, getDepthTexture, COMPAT_depth_texture, COMPAT_sRGB, getSRGB, getTextureHalfFloat, getTextureHalfFloatLinear, COMPAT_texture_half_float, COMPAT_texture_half_float_linear, COMPAT_color_buffer_half_float, getColorBufferHalfFloat, getVertexArrayObject, getDisjointTimerQuery, COMPAT_disjoint_timer_query, getNoNonInstancedActiveAttribs, getDrawBuffersIndexed, COMPAT_draw_buffers_indexed, getParallelShaderCompile, COMPAT_parallel_shader_compile, getFboRenderMipmap, COMPAT_fboRenderMipmap } from './compat';
+import { GLRenderingContext, COMPAT_instanced_arrays, COMPAT_standard_derivatives, COMPAT_vertex_array_object, getInstancedArrays, getStandardDerivatives, COMPAT_element_index_uint, getElementIndexUint, COMPAT_texture_float, getTextureFloat, COMPAT_texture_float_linear, getTextureFloatLinear, COMPAT_blend_minmax, getBlendMinMax, getFragDepth, COMPAT_frag_depth, COMPAT_color_buffer_float, getColorBufferFloat, COMPAT_draw_buffers, getDrawBuffers, getShaderTextureLod, COMPAT_shader_texture_lod, getDepthTexture, COMPAT_depth_texture, COMPAT_sRGB, getSRGB, getTextureHalfFloat, getTextureHalfFloatLinear, COMPAT_texture_half_float, COMPAT_texture_half_float_linear, COMPAT_color_buffer_half_float, getColorBufferHalfFloat, getVertexArrayObject, getDisjointTimerQuery, COMPAT_disjoint_timer_query, getNoNonInstancedActiveAttribs, getDrawBuffersIndexed, COMPAT_draw_buffers_indexed, getParallelShaderCompile, COMPAT_parallel_shader_compile, getFboRenderMipmap, COMPAT_fboRenderMipmap, COMPAT_provoking_vertex, getProvokingVertex } from './compat';
 import { isDebugMode } from '../../mol-util/debug';
 
 export type WebGLExtensions = {
@@ -29,6 +29,7 @@ export type WebGLExtensions = {
     disjointTimerQuery: COMPAT_disjoint_timer_query | null
     parallelShaderCompile: COMPAT_parallel_shader_compile | null
     fboRenderMipmap: COMPAT_fboRenderMipmap | null
+    provokingVertex: COMPAT_provoking_vertex | null
 
     noNonInstancedActiveAttribs: boolean
 }
@@ -121,6 +122,10 @@ export function createExtensions(gl: GLRenderingContext): WebGLExtensions {
     if (isDebugMode && fboRenderMipmap === null) {
         console.log('Could not find support for "fbo_render_mipmap"');
     }
+    const provokingVertex = getProvokingVertex(gl);
+    if (isDebugMode && provokingVertex === null) {
+        console.log('Could not find support for "provoking_vertex"');
+    }
 
     const noNonInstancedActiveAttribs = getNoNonInstancedActiveAttribs(gl);
 
@@ -146,6 +151,7 @@ export function createExtensions(gl: GLRenderingContext): WebGLExtensions {
         disjointTimerQuery,
         parallelShaderCompile,
         fboRenderMipmap,
+        provokingVertex,
 
         noNonInstancedActiveAttribs,
     };