Gawain: improve immediate mode performance

This was already fast on Apple, but @Severin and @dfelinto noticed slowdowns in user prefs, which is text heavy.

The problem was immBeginAtMost not being smart about VBO write flushing. immBeginAtMost can use all of its allocated range or only a subrange. The previous code was forcing back-to-back draw calls and buffer writes to serialize. This commit lets OpenGL know that our VBO writes never overlap, so there's no need to wait.

Should be much faster now!

1 files changed, 22 insertions, 7 deletions

diff --git a/source/blender/gpu/gawain/immediate.c b/source/blender/gpu/gawain/immediate.c
index 8acb9e190cf..6c4f3f0f38a 100644
--- a/source/blender/gpu/gawain/immediate.c
+++ b/source/blender/gpu/gawain/immediate.c
@@ -211,7 +211,8 @@ void immBegin(GLenum primitive, unsigned vertex_ct)
 #if APPLE_LEGACY
 	imm.buffer_data = glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY) + imm.buffer_offset;
 #else
-	imm.buffer_data = glMapBufferRange(GL_ARRAY_BUFFER, imm.buffer_offset, bytes_needed, GL_MAP_WRITE_BIT | GL_MAP_UNSYNCHRONIZED_BIT);
+	imm.buffer_data = glMapBufferRange(GL_ARRAY_BUFFER, imm.buffer_offset, bytes_needed,
+	                                   GL_MAP_WRITE_BIT | GL_MAP_UNSYNCHRONIZED_BIT | (imm.strict_vertex_ct ? 0 : GL_MAP_FLUSH_EXPLICIT_BIT));
 #endif
 
 #if TRUST_NO_ONE
@@ -341,13 +342,27 @@ void immEnd()
 		{
 #if TRUST_NO_ONE
 		assert(imm.vertex_idx <= imm.vertex_ct);
-		assert(imm.vertex_idx == 0 || vertex_count_makes_sense_for_primitive(imm.vertex_idx, imm.primitive));
 #endif
 		// printf("used %u of %u verts,", imm.vertex_idx, imm.vertex_ct);
-		imm.vertex_ct = imm.vertex_idx;
-		buffer_bytes_used = vertex_buffer_size(&imm.vertex_format, imm.vertex_ct);
-		// unused buffer bytes are available to the next immBegin
-		// printf(" %u of %u bytes\n", buffer_bytes_used, imm.buffer_bytes_mapped);
+		if (imm.vertex_idx == imm.vertex_ct)
+			{
+			buffer_bytes_used = imm.buffer_bytes_mapped;
+			}
+		else
+			{
+#if TRUST_NO_ONE
+			assert(imm.vertex_idx == 0 || vertex_count_makes_sense_for_primitive(imm.vertex_idx, imm.primitive));
+#endif
+			imm.vertex_ct = imm.vertex_idx;
+			buffer_bytes_used = vertex_buffer_size(&imm.vertex_format, imm.vertex_ct);
+			// unused buffer bytes are available to the next immBegin
+			// printf(" %u of %u bytes\n", buffer_bytes_used, imm.buffer_bytes_mapped);
+			}
+#if !APPLE_LEGACY
+		// tell OpenGL what range was modified so it doesn't copy the whole mapped range
+		// printf("flushing %u to %u\n", imm.buffer_offset, imm.buffer_offset + buffer_bytes_used - 1);
+		glFlushMappedBufferRange(GL_ARRAY_BUFFER, 0, buffer_bytes_used);
+#endif
 		}
 
 #if IMM_BATCH_COMBO
@@ -367,8 +382,8 @@ void immEnd()
 		{
 #if APPLE_LEGACY
 		// tell OpenGL what range was modified so it doesn't copy the whole buffer
+		// printf("flushing %u to %u\n", imm.buffer_offset, imm.buffer_offset + buffer_bytes_used - 1);
 		glFlushMappedBufferRangeAPPLE(GL_ARRAY_BUFFER, imm.buffer_offset, buffer_bytes_used);
-//		printf("flushing %u to %u\n", imm.buffer_offset, imm.buffer_offset + buffer_bytes_used - 1);
 #endif
 		glUnmapBuffer(GL_ARRAY_BUFFER);