Hair Particle: Fix issue on OSX due to hardware accelerated subdivision

Workaround to tranform feedback not working on mac.
On some system it crashes (see T58489) and on some other it outputs
garbage (see T60171).

So instead of using transform feedback we render to a texture,
readback the result to system memory and reupload as VBO data.
It is really not ideal performance wise, but it is the simplest
and the most local workaround that still uses the power of the GPU.

This should fix T59426, T60171 and T58489.

1 files changed, 98 insertions, 2 deletions

diff --git a/source/blender/draw/intern/draw_hair.c b/source/blender/draw/intern/draw_hair.c
index ace85eb1ffe..7c086c5ec93 100644
--- a/source/blender/draw/intern/draw_hair.c
+++ b/source/blender/draw/intern/draw_hair.c
@@ -40,16 +40,33 @@
 
 #include "draw_hair_private.h"
 
+#ifndef __APPLE__
+#  define USE_TRANSFORM_FEEDBACK
+#endif
+
 typedef enum ParticleRefineShader {
 	PART_REFINE_CATMULL_ROM = 0,
 	PART_REFINE_MAX_SHADER,
 } ParticleRefineShader;
 
+#ifndef USE_TRANSFORM_FEEDBACK
+typedef struct ParticleRefineCall {
+	struct ParticleRefineCall *next;
+	GPUVertBuf *vbo;
+	DRWShadingGroup *shgrp;
+	uint vert_len;
+} ParticleRefineCall;
+
+static ParticleRefineCall *g_tf_calls = NULL;
+static int g_tf_target_height;
+#endif
+
 static GPUShader *g_refine_shaders[PART_REFINE_MAX_SHADER] = {NULL};
 static DRWPass *g_tf_pass; /* XXX can be a problem with multiple DRWManager in the future */
 
 extern char datatoc_common_hair_lib_glsl[];
 extern char datatoc_common_hair_refine_vert_glsl[];
+extern char datatoc_gpu_shader_3D_smooth_color_frag_glsl[];
 
 static GPUShader *hair_refine_shader_get(ParticleRefineShader sh)
 {
@@ -59,10 +76,17 @@ static GPUShader *hair_refine_shader_get(ParticleRefineShader sh)
 
 	char *vert_with_lib = BLI_string_joinN(datatoc_common_hair_lib_glsl, datatoc_common_hair_refine_vert_glsl);
 
-	const char *var_names[1] = {"outData"};
-
+#ifdef USE_TRANSFORM_FEEDBACK
+	const char *var_names[1] = {"finalColor"};
 	g_refine_shaders[sh] = DRW_shader_create_with_transform_feedback(vert_with_lib, NULL, "#define HAIR_PHASE_SUBDIV\n",
 	                                                                 GPU_SHADER_TFB_POINTS, var_names, 1);
+#else
+	g_refine_shaders[sh] = DRW_shader_create(
+	       vert_with_lib, NULL,
+	       datatoc_gpu_shader_3D_smooth_color_frag_glsl,
+	       "#define HAIR_PHASE_SUBDIV\n"
+	       "#define TF_WORKAROUND\n");
+#endif
 
 	MEM_freeN(vert_with_lib);
 
@@ -71,7 +95,11 @@ static GPUShader *hair_refine_shader_get(ParticleRefineShader sh)
 
 void DRW_hair_init(void)
 {
+#ifdef USE_TRANSFORM_FEEDBACK
 	g_tf_pass = DRW_pass_create("Update Hair Pass", DRW_STATE_TRANS_FEEDBACK);
+#else
+	g_tf_pass = DRW_pass_create("Update Hair Pass", DRW_STATE_WRITE_COLOR | DRW_STATE_POINT);
+#endif
 }
 
 typedef struct DRWHairInstanceData {
@@ -162,8 +190,22 @@ static DRWShadingGroup *drw_shgroup_create_hair_procedural_ex(
 	if (need_ft_update) {
 		int final_points_len = hair_cache->final[subdiv].strands_res * hair_cache->strands_len;
 		GPUShader *tf_shader = hair_refine_shader_get(PART_REFINE_CATMULL_ROM);
+
+#ifdef USE_TRANSFORM_FEEDBACK
 		DRWShadingGroup *tf_shgrp = DRW_shgroup_transform_feedback_create(tf_shader, g_tf_pass,
 		                                                                  hair_cache->final[subdiv].proc_buf);
+#else
+		DRWShadingGroup *tf_shgrp = DRW_shgroup_create(tf_shader, g_tf_pass);
+
+		ParticleRefineCall *pr_call = MEM_mallocN(sizeof(*pr_call), __func__);
+		pr_call->next = g_tf_calls;
+		pr_call->vbo = hair_cache->final[subdiv].proc_buf;
+		pr_call->shgrp = tf_shgrp;
+		pr_call->vert_len = final_points_len;
+		g_tf_calls = pr_call;
+		DRW_shgroup_uniform_int(tf_shgrp, "targetHeight", &g_tf_target_height, 1);
+#endif
+
 		DRW_shgroup_uniform_texture(tf_shgrp, "hairPointBuffer", hair_cache->point_tex);
 		DRW_shgroup_uniform_texture(tf_shgrp, "hairStrandBuffer", hair_cache->strand_tex);
 		DRW_shgroup_uniform_int(tf_shgrp, "hairStrandsRes", &hair_cache->final[subdiv].strands_res, 1);
@@ -191,7 +233,61 @@ DRWShadingGroup *DRW_shgroup_material_hair_create(
 
 void DRW_hair_update(void)
 {
+#ifndef USE_TRANSFORM_FEEDBACK
+	/**
+	 * Workaround to tranform feedback not working on mac.
+	 * On some system it crashes (see T58489) and on some other it renders garbage (see T60171).
+	 *
+	 * So instead of using transform feedback we render to a texture,
+	 * readback the result to system memory and reupload as VBO data.
+	 * It is really not ideal performance wise, but it is the simplest
+	 * and the most local workaround that still uses the power of the GPU.
+	 **/
+
+	if (g_tf_calls == NULL) {
+		return;
+	}
+
+	/* Search ideal buffer size. */
+	uint max_size = 0;
+	for (ParticleRefineCall *pr_call = g_tf_calls; pr_call; pr_call = pr_call->next) {
+		max_size = max_ii(max_size, pr_call->vert_len);
+	}
+
+	/* Create target Texture / Framebuffer */
+	int height = (1 + max_size / 8192);
+	GPUTexture *tex = DRW_texture_pool_query_2D(8192, height, GPU_RGBA32F, (void *)DRW_hair_update);
+	g_tf_target_height = height;
+
+	GPUFrameBuffer *fb = NULL;
+	GPU_framebuffer_ensure_config(&fb, {
+		GPU_ATTACHMENT_NONE,
+		GPU_ATTACHMENT_TEXTURE(tex),
+	});
+
+	float *data = MEM_mallocN(sizeof(float) * 4 * 8192 * height, "tf fallback buffer");
+
+	GPU_framebuffer_bind(fb);
+	while (g_tf_calls != NULL) {
+		ParticleRefineCall *pr_call = g_tf_calls;
+		g_tf_calls = g_tf_calls->next;
+		DRW_draw_pass_subset(g_tf_pass, pr_call->shgrp, pr_call->shgrp);
+		/* Readback result to main memory. */
+		GPU_framebuffer_read_color(fb, 0, 0, 8192, height, 4, 0, data);
+		/* Upload back to VBO. */
+		GPU_vertbuf_use(pr_call->vbo);
+		glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(float) * 4 * pr_call->vert_len, data);
+
+		MEM_freeN(pr_call);
+	}
+
+	MEM_freeN(data);
+	GPU_framebuffer_free(fb);
+#else
+	/* TODO(fclem): replace by compute shader. */
+	/* Just render using transform feedback. */
 	DRW_draw_pass(g_tf_pass);
+#endif
 }
 
 void DRW_hair_free(void)