Fix T57455: Laggy, freezing UI with Linux and Intel UHD 620

Seems like a driver bug but doing glFlush() before these calls fixes it.

source/blender/editors/screen/screen_draw.c

@@ -387,6 +387,12 @@ void ED_screen_draw_edges(wmWindow *win)
 		BLI_rcti_do_minmax_v(&scissor_rect, (int[2]){sa->v3->vec.x, sa->v3->vec.y});
 	}
 
+	if (GPU_type_matches(GPU_DEVICE_INTEL_UHD, GPU_OS_UNIX, GPU_OS_ANY)) {
+		/* For some reason, on linux + Intel UHD Graphics 620 the driver
+		 * hangs if we don't flush before this. (See T57455) */
+		glFlush();
+	}
+
 	GPU_scissor(scissor_rect.xmin,
 	            scissor_rect.ymin,
 	            BLI_rcti_size_x(&scissor_rect) + 1,

source/blender/gpu/GPU_extensions.h

@@ -66,8 +66,9 @@ typedef enum GPUDeviceType {
 	GPU_DEVICE_NVIDIA =     (1 << 0),
 	GPU_DEVICE_ATI =        (1 << 1),
 	GPU_DEVICE_INTEL =      (1 << 2),
-	GPU_DEVICE_SOFTWARE =   (1 << 3),
-	GPU_DEVICE_UNKNOWN =    (1 << 4),
+	GPU_DEVICE_INTEL_UHD =  (1 << 3),
+	GPU_DEVICE_SOFTWARE =   (1 << 4),
+	GPU_DEVICE_UNKNOWN =    (1 << 5),
 	GPU_DEVICE_ANY =        (0xff)
 } GPUDeviceType;
 

source/blender/gpu/intern/gpu_extensions.c

@@ -282,6 +282,10 @@ void gpu_extensions_init(void)
 	{
 		GG.device = GPU_DEVICE_INTEL;
 		GG.driver = GPU_DRIVER_OFFICIAL;
+
+		if (strstr(renderer, "UHD Graphics")) {
+			GG.device |= GPU_DEVICE_INTEL_UHD;
+		}
 	}
 	else if ((strstr(renderer, "Mesa DRI R")) ||
 	         (strstr(renderer, "Radeon") && strstr(vendor, "X.Org")) ||