GPU: Add GPU_vertformat_triple_load to load next vertices attrib

Right now does not add padding at the end of the buffer.

This seems not necessary but may cause problem on some platform. If needed
we will add this padding (only 2 more vertices).

2 files changed, 63 insertions, 6 deletions

diff --git a/source/blender/gpu/GPU_vertex_format.h b/source/blender/gpu/GPU_vertex_format.h
index 113a3e894d0..7a271caf079 100644
--- a/source/blender/gpu/GPU_vertex_format.h
+++ b/source/blender/gpu/GPU_vertex_format.h
@@ -92,6 +92,16 @@ uint GPU_vertformat_attr_add(
 void GPU_vertformat_alias_add(GPUVertFormat *, const char *alias);
 int GPU_vertformat_attr_id_get(const GPUVertFormat *, const char *name);
 
+/**
+ * This makes the "virtual" attribs with suffixes "0", "1", "2" to access triangle data in the vertex
+ * shader.
+ *
+ * IMPORTANT:
+ * - Call this before creating the vertex buffer and after creating all attributes
+ * - Only first vertex out of 3 has the correct information. Use flat output with GL_FIRST_VERTEX_CONVENTION.
+ **/
+void GPU_vertformat_triple_load(GPUVertFormat *format);
+
 /* format conversion */
 
 typedef struct GPUPackedNormal {
diff --git a/source/blender/gpu/intern/gpu_vertex_format.c b/source/blender/gpu/intern/gpu_vertex_format.c
index c3de3d52b47..ca636d2e231 100644
--- a/source/blender/gpu/intern/gpu_vertex_format.c
+++ b/source/blender/gpu/intern/gpu_vertex_format.c
@@ -128,7 +128,7 @@ uint vertex_buffer_size(const GPUVertFormat *format, uint vertex_len)
 	return format->stride * vertex_len;
 }
 
-static const char *copy_attrib_name(GPUVertFormat *format, const char *name)
+static const char *copy_attrib_name(GPUVertFormat *format, const char *name, const char *suffix)
 {
 	/* strncpy does 110% of what we need; let's do exactly 100% */
 	char *name_copy = format->names + format->name_offset;
@@ -139,8 +139,21 @@ static const char *copy_attrib_name(GPUVertFormat *format, const char *name)
 		const char c = name[i];
 		name_copy[i] = c;
 		if (c == '\0') {
-			terminated = true;
-			format->name_offset += (i + 1);
+			if (suffix) {
+				for (uint j = 0; j < available; ++j) {
+					const char s = suffix[j];
+					name_copy[i + j] = s;
+					if (s == '\0') {
+						terminated = true;
+						format->name_offset += (i + j + 1);
+						break;
+					}
+				}
+			}
+			else {
+				terminated = true;
+				format->name_offset += (i + 1);
+			}
 			break;
 		}
 	}
@@ -186,7 +199,7 @@ uint GPU_vertformat_attr_add(
 	const uint attrib_id = format->attr_len++;
 	GPUVertAttr *attrib = format->attribs + attrib_id;
 
-	attrib->name[attrib->name_len++] = copy_attrib_name(format, name);
+	attrib->name[attrib->name_len++] = copy_attrib_name(format, name, NULL);
 	attrib->comp_type = comp_type;
 	attrib->gl_comp_type = convert_comp_type_to_gl(comp_type);
 	attrib->comp_len = (comp_type == GPU_COMP_I10) ? 4 : comp_len; /* system needs 10_10_10_2 to be 4 or BGRA */
@@ -205,7 +218,7 @@ void GPU_vertformat_alias_add(GPUVertFormat *format, const char *alias)
 	assert(attrib->name_len < GPU_VERT_ATTR_MAX_NAMES);
 #endif
 	format->name_len++; /* multiname support */
-	attrib->name[attrib->name_len++] = copy_attrib_name(format, alias);
+	attrib->name[attrib->name_len++] = copy_attrib_name(format, alias, NULL);
 }
 
 int GPU_vertformat_attr_id_get(const GPUVertFormat *format, const char *name)
@@ -221,6 +234,40 @@ int GPU_vertformat_attr_id_get(const GPUVertFormat *format, const char *name)
 	return -1;
 }
 
+void GPU_vertformat_triple_load(GPUVertFormat *format)
+{
+#if TRUST_NO_ONE
+	assert(!format->packed);
+	assert(format->attr_len * 3 < GPU_VERT_ATTR_MAX_LEN);
+	assert(format->name_len + format->attr_len * 3 < GPU_VERT_ATTR_MAX_LEN);
+#endif
+
+	VertexFormat_pack(format);
+
+	uint old_attr_len = format->attr_len;
+	for (uint a_idx = 0; a_idx < old_attr_len; ++a_idx) {
+		GPUVertAttr *attrib = format->attribs + a_idx;
+		/* Duplicate attrib twice */
+		for (int i = 1; i < 3; ++i) {
+			GPUVertAttr *dst_attrib = format->attribs + format->attr_len;
+			memcpy(dst_attrib, attrib, sizeof(GPUVertAttr));
+			/* Increase offset to the next vertex. */
+			dst_attrib->offset += format->stride * i;
+			/* Only copy first name for now. */
+			dst_attrib->name_len = 0;
+			dst_attrib->name[dst_attrib->name_len++] = copy_attrib_name(format, attrib->name[0], (i == 1) ? "1" : "2");
+			format->attr_len++;
+		}
+
+#if TRUST_NO_ONE
+		assert(attrib->name_len < GPU_VERT_ATTR_MAX_NAMES);
+#endif
+		/* Add alias to first attrib. */
+		format->name_len++;
+		attrib->name[attrib->name_len++] = copy_attrib_name(format, attrib->name[0], "0");
+	}
+}
+
 uint padding(uint offset, uint alignment)
 {
 	const uint mod = offset % alignment;
@@ -380,7 +427,7 @@ void GPU_vertformat_from_interface(GPUVertFormat *format, const GPUShaderInterfa
 
 			GPUVertAttr *attrib = format->attribs + input->location;
 
-			attrib->name[attrib->name_len++] = copy_attrib_name(format, name_buffer + input->name_offset);
+			attrib->name[attrib->name_len++] = copy_attrib_name(format, name_buffer + input->name_offset, NULL);
 			attrib->offset = 0; /* offsets & stride are calculated later (during pack) */
 			attrib->comp_len = calc_input_component_size(input);
 			attrib->sz = attrib->comp_len * 4;