Fix crash running GPU shader.format_calc() with attributes like gl_VertexID

When using opengl attributes such as gl_VertexID in a shader its
location is set to -1. This location was used without checking in an
attribute array. This fails big time when called from python. For
example `print(shader.format_calc())` made python crash immediately.

this fixes https://github.com/JacquesLucke/animation_nodes/issues/1141

Reviewed By: fclem, brecht

Differential Revision: https://developer.blender.org/D5231

1 files changed, 5 insertions, 0 deletions

diff --git a/source/blender/gpu/intern/gpu_vertex_format.c b/source/blender/gpu/intern/gpu_vertex_format.c
index 37e1f9cf9da..e745c525df6 100644
--- a/source/blender/gpu/intern/gpu_vertex_format.c
+++ b/source/blender/gpu/intern/gpu_vertex_format.c
@@ -365,6 +365,11 @@ void GPU_vertformat_from_interface(GPUVertFormat *format, const GPUShaderInterfa
       input = next;
       next = input->next;
 
+      /* OpenGL attributes such as `gl_VertexID` have a location of -1. */
+      if (input->location < 0) {
+        continue;
+      }
+
       format->name_len++; /* multiname support */
       format->attr_len++;