GPU: Avoid undocumented/fragile dependency on shader enumerator order

Previously this was using `GPU_SHADER_TEXT` as default value indicating
an "unset" state. This wasn't documented in the definition (and so
D16284 added a new enumerator that broke this). Plus code was assuming
this enumerator would always have the value 0 without specifying this in
the definition either.

In this case it's easy to not rely on the enum value at all, and just
use `std::optional` to add a "unset" state.

Differential Revision: https://developer.blender.org/D16303

1 files changed, 5 insertions, 3 deletions

diff --git a/source/blender/gpu/intern/gpu_immediate_private.hh b/source/blender/gpu/intern/gpu_immediate_private.hh
index 74ebbdc7ae3..c4e11e7082b 100644
--- a/source/blender/gpu/intern/gpu_immediate_private.hh
+++ b/source/blender/gpu/intern/gpu_immediate_private.hh
@@ -9,6 +9,8 @@
 
 #pragma once
 
+#include <optional>
+
 #include "GPU_batch.h"
 #include "GPU_primitive.h"
 #include "GPU_shader.h"
@@ -42,9 +44,9 @@ class Immediate {
   /** Wide Line workaround. */
 
   /** Previously bound shader to restore after drawing. */
-  eGPUBuiltinShader prev_builtin_shader = GPU_SHADER_TEXT;
-  /** Builtin shader index. Used to test if the workaround can be done. */
-  eGPUBuiltinShader builtin_shader_bound = GPU_SHADER_TEXT;
+  std::optional<eGPUBuiltinShader> prev_builtin_shader;
+  /** Builtin shader index. Used to test if the line width workaround can be done. */
+  std::optional<eGPUBuiltinShader> builtin_shader_bound;
   /** Uniform color: Kept here to update the wide-line shader just before #immBegin. */
   float uniform_color[4];