Fix T60171: Hair Particles Not Displaying in Viewport

This patch fixes T60171 by adding a dummy read from the `dummy` vertex attribute to `hair_get_pos_tan_binor_time` in `common_hair_lib.glsl`. Confirmed to work on my machine (macOS 10.14.4 Beta, Radeon R​9 M295X).

According to my experiments regarding this issue, the problem is triggered when all of the following conditions are met: (a) the shader has no vertex reads; (b) the index buffer is ≥ 256KiB. I can't really give an explanation of this misbehavior because of the video driver's closed-source nature.

Reviewers: fclem

Reviewed By: fclem

Subscribers: zeddb

Maniphest Tasks: T60171

Differential Revision: https://developer.blender.org/D4490

1 files changed, 11 insertions, 0 deletions

diff --git a/source/blender/draw/modes/shaders/common_hair_lib.glsl b/source/blender/draw/modes/shaders/common_hair_lib.glsl
index 359e4d87b7a..4c540d2b478 100644
--- a/source/blender/draw/modes/shaders/common_hair_lib.glsl
+++ b/source/blender/draw/modes/shaders/common_hair_lib.glsl
@@ -136,6 +136,10 @@ float hair_shaperadius(float shape, float root, float tip, float time)
 	return (radius * (root - tip)) + tip;
 }
 
+#ifdef OS_MAC
+in float dummy;
+#endif
+
 void hair_get_pos_tan_binor_time(
         bool is_persp, mat4 invmodel_mat, vec3 camera_pos, vec3 camera_z,
         out vec3 wpos, out vec3 wtan, out vec3 wbinor, out float time, out float thickness, out float thick_time)
@@ -144,6 +148,13 @@ void hair_get_pos_tan_binor_time(
 	vec4 data = texelFetch(hairPointBuffer, id);
 	wpos = data.point_position;
 	time = data.point_time;
+
+#ifdef OS_MAC
+	/* Generate a dummy read to avoid the driver bug with shaders having no
+	 * vertex reads on macOS (T60171) */
+	wpos.y += dummy * 0.0;
+#endif
+
 	if (time == 0.0) {
 		/* Hair root */
 		wtan = texelFetch(hairPointBuffer, id + 1).point_position - wpos;