GLES2: Make Nvidia flicker workaround opt-in

It has a big impact on 2D and text rendering performance (cf. #24466)
so the solution seems worse than the bug it aims to work around.

It's now opt-in via "rendering/quality/2d/gles2_use_nvidia_rect_flicker_workaround"
for those who need it and have a simple enough game for the performance
drop not to be an issue.

Fixes #24466.

2 files changed, 130 insertions, 119 deletions

diff --git a/drivers/gles2/rasterizer_canvas_gles2.cpp b/drivers/gles2/rasterizer_canvas_gles2.cpp
index 2152810e8f..b008e18f67 100644
--- a/drivers/gles2/rasterizer_canvas_gles2.cpp
+++ b/drivers/gles2/rasterizer_canvas_gles2.cpp
@@ -489,161 +489,164 @@ void RasterizerCanvasGLES2::_canvas_item_render_commands(Item *p_item, Item *cur
 				glDisableVertexAttribArray(VS::ARRAY_COLOR);
 				glVertexAttrib4fv(VS::ARRAY_COLOR, r->modulate.components);
 
-//use a more compatible workaround, as this does not fail on nvidia
-#ifdef GLES_OVER_GL
-				//more compatible
-				state.canvas_shader.set_conditional(CanvasShaderGLES2::USE_TEXTURE_RECT, false);
-
-				if (state.canvas_shader.bind()) {
-					_set_uniforms();
-					state.canvas_shader.use_material((void *)p_material);
-				}
+				// On some widespread Nvidia cards, the normal draw method can produce some
+				// flickering in draw_rect and especially TileMap rendering (tiles randomly flicker).
+				// See GH-9913.
+				// To work it around, we use a simpler draw method which does not flicker, but gives
+				// a non negligible performance hit, so it's opt-in (GH-24466).
+				if (use_nvidia_rect_workaround) {
+					state.canvas_shader.set_conditional(CanvasShaderGLES2::USE_TEXTURE_RECT, false);
+
+					if (state.canvas_shader.bind()) {
+						_set_uniforms();
+						state.canvas_shader.use_material((void *)p_material);
+					}
 
-				Vector2 points[4] = {
-					r->rect.position,
-					r->rect.position + Vector2(r->rect.size.x, 0.0),
-					r->rect.position + r->rect.size,
-					r->rect.position + Vector2(0.0, r->rect.size.y),
-				};
+					Vector2 points[4] = {
+						r->rect.position,
+						r->rect.position + Vector2(r->rect.size.x, 0.0),
+						r->rect.position + r->rect.size,
+						r->rect.position + Vector2(0.0, r->rect.size.y),
+					};
 
-				if (r->rect.size.x < 0) {
-					SWAP(points[0], points[1]);
-					SWAP(points[2], points[3]);
-				}
-				if (r->rect.size.y < 0) {
-					SWAP(points[0], points[3]);
-					SWAP(points[1], points[2]);
-				}
+					if (r->rect.size.x < 0) {
+						SWAP(points[0], points[1]);
+						SWAP(points[2], points[3]);
+					}
+					if (r->rect.size.y < 0) {
+						SWAP(points[0], points[3]);
+						SWAP(points[1], points[2]);
+					}
 
-				RasterizerStorageGLES2::Texture *texture = _bind_canvas_texture(r->texture, r->normal_map);
+					RasterizerStorageGLES2::Texture *texture = _bind_canvas_texture(r->texture, r->normal_map);
 
-				if (texture) {
-					Size2 texpixel_size(1.0 / texture->width, 1.0 / texture->height);
+					if (texture) {
+						Size2 texpixel_size(1.0 / texture->width, 1.0 / texture->height);
 
-					Rect2 src_rect = (r->flags & CANVAS_RECT_REGION) ? Rect2(r->source.position * texpixel_size, r->source.size * texpixel_size) : Rect2(0, 0, 1, 1);
+						Rect2 src_rect = (r->flags & CANVAS_RECT_REGION) ? Rect2(r->source.position * texpixel_size, r->source.size * texpixel_size) : Rect2(0, 0, 1, 1);
 
-					Vector2 uvs[4] = {
-						src_rect.position,
-						src_rect.position + Vector2(src_rect.size.x, 0.0),
-						src_rect.position + src_rect.size,
-						src_rect.position + Vector2(0.0, src_rect.size.y),
-					};
+						Vector2 uvs[4] = {
+							src_rect.position,
+							src_rect.position + Vector2(src_rect.size.x, 0.0),
+							src_rect.position + src_rect.size,
+							src_rect.position + Vector2(0.0, src_rect.size.y),
+						};
 
-					if (r->flags & CANVAS_RECT_TRANSPOSE) {
-						SWAP(uvs[1], uvs[3]);
-					}
+						if (r->flags & CANVAS_RECT_TRANSPOSE) {
+							SWAP(uvs[1], uvs[3]);
+						}
 
-					if (r->flags & CANVAS_RECT_FLIP_H) {
-						SWAP(uvs[0], uvs[1]);
-						SWAP(uvs[2], uvs[3]);
-					}
-					if (r->flags & CANVAS_RECT_FLIP_V) {
-						SWAP(uvs[0], uvs[3]);
-						SWAP(uvs[1], uvs[2]);
-					}
+						if (r->flags & CANVAS_RECT_FLIP_H) {
+							SWAP(uvs[0], uvs[1]);
+							SWAP(uvs[2], uvs[3]);
+						}
+						if (r->flags & CANVAS_RECT_FLIP_V) {
+							SWAP(uvs[0], uvs[3]);
+							SWAP(uvs[1], uvs[2]);
+						}
 
-					state.canvas_shader.set_uniform(CanvasShaderGLES2::COLOR_TEXPIXEL_SIZE, texpixel_size);
+						state.canvas_shader.set_uniform(CanvasShaderGLES2::COLOR_TEXPIXEL_SIZE, texpixel_size);
 
-					bool untile = false;
+						bool untile = false;
 
-					if (r->flags & CANVAS_RECT_TILE && !(texture->flags & VS::TEXTURE_FLAG_REPEAT)) {
-						glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
-						glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
-						untile = true;
-					}
+						if (r->flags & CANVAS_RECT_TILE && !(texture->flags & VS::TEXTURE_FLAG_REPEAT)) {
+							glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
+							glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
+							untile = true;
+						}
 
-					_draw_gui_primitive(4, points, NULL, uvs);
+						_draw_gui_primitive(4, points, NULL, uvs);
 
-					if (untile) {
-						glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
-						glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+						if (untile) {
+							glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+							glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+						}
+					} else {
+						state.canvas_shader.set_uniform(CanvasShaderGLES2::COLOR_TEXPIXEL_SIZE, Vector2());
+						_draw_gui_primitive(4, points, NULL, NULL);
 					}
-				} else {
-					state.canvas_shader.set_uniform(CanvasShaderGLES2::COLOR_TEXPIXEL_SIZE, Vector2());
-					_draw_gui_primitive(4, points, NULL, NULL);
-				}
 
-#else
-				//disabled because it fails on buggy nvidia drivers
-				_bind_quad_buffer();
+				} else {
+					// This branch is better for performance, but can produce flicker on Nvidia, see above comment.
+					_bind_quad_buffer();
 
-				state.canvas_shader.set_conditional(CanvasShaderGLES2::USE_TEXTURE_RECT, true);
+					state.canvas_shader.set_conditional(CanvasShaderGLES2::USE_TEXTURE_RECT, true);
 
-				if (state.canvas_shader.bind()) {
-					_set_uniforms();
-					state.canvas_shader.use_material((void *)p_material);
-				}
+					if (state.canvas_shader.bind()) {
+						_set_uniforms();
+						state.canvas_shader.use_material((void *)p_material);
+					}
 
-				RasterizerStorageGLES2::Texture *tex = _bind_canvas_texture(r->texture, r->normal_map);
+					RasterizerStorageGLES2::Texture *tex = _bind_canvas_texture(r->texture, r->normal_map);
 
-				if (!tex) {
-					Rect2 dst_rect = Rect2(r->rect.position, r->rect.size);
+					if (!tex) {
+						Rect2 dst_rect = Rect2(r->rect.position, r->rect.size);
 
-					if (dst_rect.size.width < 0) {
-						dst_rect.position.x += dst_rect.size.width;
-						dst_rect.size.width *= -1;
-					}
-					if (dst_rect.size.height < 0) {
-						dst_rect.position.y += dst_rect.size.height;
-						dst_rect.size.height *= -1;
-					}
+						if (dst_rect.size.width < 0) {
+							dst_rect.position.x += dst_rect.size.width;
+							dst_rect.size.width *= -1;
+						}
+						if (dst_rect.size.height < 0) {
+							dst_rect.position.y += dst_rect.size.height;
+							dst_rect.size.height *= -1;
+						}
 
-					state.canvas_shader.set_uniform(CanvasShaderGLES2::DST_RECT, Color(dst_rect.position.x, dst_rect.position.y, dst_rect.size.x, dst_rect.size.y));
-					state.canvas_shader.set_uniform(CanvasShaderGLES2::SRC_RECT, Color(0, 0, 1, 1));
+						state.canvas_shader.set_uniform(CanvasShaderGLES2::DST_RECT, Color(dst_rect.position.x, dst_rect.position.y, dst_rect.size.x, dst_rect.size.y));
+						state.canvas_shader.set_uniform(CanvasShaderGLES2::SRC_RECT, Color(0, 0, 1, 1));
 
-					glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
-				} else {
+						glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
+					} else {
 
-					bool untile = false;
+						bool untile = false;
 
-					if (r->flags & CANVAS_RECT_TILE && !(tex->flags & VS::TEXTURE_FLAG_REPEAT)) {
-						glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
-						glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
-						untile = true;
-					}
+						if (r->flags & CANVAS_RECT_TILE && !(tex->flags & VS::TEXTURE_FLAG_REPEAT)) {
+							glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
+							glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
+							untile = true;
+						}
 
-					Size2 texpixel_size(1.0 / tex->width, 1.0 / tex->height);
-					Rect2 src_rect = (r->flags & CANVAS_RECT_REGION) ? Rect2(r->source.position * texpixel_size, r->source.size * texpixel_size) : Rect2(0, 0, 1, 1);
+						Size2 texpixel_size(1.0 / tex->width, 1.0 / tex->height);
+						Rect2 src_rect = (r->flags & CANVAS_RECT_REGION) ? Rect2(r->source.position * texpixel_size, r->source.size * texpixel_size) : Rect2(0, 0, 1, 1);
 
-					Rect2 dst_rect = Rect2(r->rect.position, r->rect.size);
+						Rect2 dst_rect = Rect2(r->rect.position, r->rect.size);
 
-					if (dst_rect.size.width < 0) {
-						dst_rect.position.x += dst_rect.size.width;
-						dst_rect.size.width *= -1;
-					}
-					if (dst_rect.size.height < 0) {
-						dst_rect.position.y += dst_rect.size.height;
-						dst_rect.size.height *= -1;
-					}
+						if (dst_rect.size.width < 0) {
+							dst_rect.position.x += dst_rect.size.width;
+							dst_rect.size.width *= -1;
+						}
+						if (dst_rect.size.height < 0) {
+							dst_rect.position.y += dst_rect.size.height;
+							dst_rect.size.height *= -1;
+						}
 
-					if (r->flags & CANVAS_RECT_FLIP_H) {
-						src_rect.size.x *= -1;
-					}
+						if (r->flags & CANVAS_RECT_FLIP_H) {
+							src_rect.size.x *= -1;
+						}
 
-					if (r->flags & CANVAS_RECT_FLIP_V) {
-						src_rect.size.y *= -1;
-					}
+						if (r->flags & CANVAS_RECT_FLIP_V) {
+							src_rect.size.y *= -1;
+						}
 
-					if (r->flags & CANVAS_RECT_TRANSPOSE) {
-						dst_rect.size.x *= -1; // Encoding in the dst_rect.z uniform
-					}
+						if (r->flags & CANVAS_RECT_TRANSPOSE) {
+							dst_rect.size.x *= -1; // Encoding in the dst_rect.z uniform
+						}
 
-					state.canvas_shader.set_uniform(CanvasShaderGLES2::COLOR_TEXPIXEL_SIZE, texpixel_size);
+						state.canvas_shader.set_uniform(CanvasShaderGLES2::COLOR_TEXPIXEL_SIZE, texpixel_size);
 
-					state.canvas_shader.set_uniform(CanvasShaderGLES2::DST_RECT, Color(dst_rect.position.x, dst_rect.position.y, dst_rect.size.x, dst_rect.size.y));
-					state.canvas_shader.set_uniform(CanvasShaderGLES2::SRC_RECT, Color(src_rect.position.x, src_rect.position.y, src_rect.size.x, src_rect.size.y));
+						state.canvas_shader.set_uniform(CanvasShaderGLES2::DST_RECT, Color(dst_rect.position.x, dst_rect.position.y, dst_rect.size.x, dst_rect.size.y));
+						state.canvas_shader.set_uniform(CanvasShaderGLES2::SRC_RECT, Color(src_rect.position.x, src_rect.position.y, src_rect.size.x, src_rect.size.y));
 
-					glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
+						glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
 
-					if (untile) {
-						glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
-						glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+						if (untile) {
+							glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+							glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+						}
 					}
-				}
 
-				glBindBuffer(GL_ARRAY_BUFFER, 0);
-				glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
-#endif
+					glBindBuffer(GL_ARRAY_BUFFER, 0);
+					glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
+				}
 			} break;
 
 			case Item::Command::TYPE_NINEPATCH: {
@@ -1856,4 +1859,10 @@ void RasterizerCanvasGLES2::finalize() {
 }
 
 RasterizerCanvasGLES2::RasterizerCanvasGLES2() {
+#ifdef GLES_OVER_GL
+	use_nvidia_rect_workaround = GLOBAL_GET("rendering/quality/2d/gles2_use_nvidia_rect_flicker_workaround");
+#else
+	// Not needed (a priori) on GLES devices
+	use_nvidia_rect_workaround = false;
+#endif
 }
diff --git a/drivers/gles2/rasterizer_canvas_gles2.h b/drivers/gles2/rasterizer_canvas_gles2.h
index ddb72d1c63..221427198a 100644
--- a/drivers/gles2/rasterizer_canvas_gles2.h
+++ b/drivers/gles2/rasterizer_canvas_gles2.h
@@ -102,6 +102,8 @@ public:
 
 	RasterizerStorageGLES2 *storage;
 
+	bool use_nvidia_rect_workaround;
+
 	virtual RID light_internal_create();
 	virtual void light_internal_update(RID p_rid, Light *p_light);
 	virtual void light_internal_free(RID p_rid);