GPU: Add support for stencil buffer texturing mode.

This adds the possibility to read the stencil buffer inside shaders.
This is only available on GL 4.3 so use it accordingly.

source/blender/gpu/GPU_texture.h

@@ -299,6 +299,11 @@ void GPU_texture_filter_mode(GPUTexture *tex, bool use_filter);
 void GPU_texture_mipmap_mode(GPUTexture *tex, bool use_mipmap, bool use_filter);
 void GPU_texture_wrap_mode(GPUTexture *tex, bool use_repeat, bool use_clamp);
 void GPU_texture_swizzle_set(GPUTexture *tex, const char swizzle[4]);
+/**
+ * Set depth stencil texture sampling behavior. Can work on texture views.
+ * If stencil sampling is enabled, an unsigned integer sampler is required.
+ */
+void GPU_texture_stencil_texture_mode_set(GPUTexture *tex, bool use_stencil);
 
 /**
  * Return the number of dimensions of the texture ignoring dimension of layers (1, 2 or 3).

source/blender/gpu/intern/gpu_texture.cc

@@ -550,6 +550,12 @@ void GPU_texture_swizzle_set(GPUTexture *tex, const char swizzle[4])
   reinterpret_cast<Texture *>(tex)->swizzle_set(swizzle);
 }
 
+void GPU_texture_stencil_texture_mode_set(GPUTexture *tex, bool use_stencil)
+{
+  BLI_assert(GPU_texture_stencil(tex) || !use_stencil);
+  reinterpret_cast<Texture *>(tex)->stencil_texture_mode_set(use_stencil);
+}
+
 void GPU_texture_free(GPUTexture *tex_)
 {
   Texture *tex = reinterpret_cast<Texture *>(tex_);

source/blender/gpu/intern/gpu_texture_private.hh

@@ -117,6 +117,7 @@ class Texture {
   virtual void copy_to(Texture *tex) = 0;
   virtual void clear(eGPUDataFormat format, const void *data) = 0;
   virtual void swizzle_set(const char swizzle_mask[4]) = 0;
+  virtual void stencil_texture_mode_set(bool use_stencil) = 0;
   virtual void mip_range_set(int min, int max) = 0;
   virtual void *read(int mip, eGPUDataFormat format) = 0;
 

source/blender/gpu/opengl/gl_backend.cc

@@ -444,6 +444,7 @@ bool GLContext::native_barycentric_support = false;
 bool GLContext::multi_bind_support = false;
 bool GLContext::multi_draw_indirect_support = false;
 bool GLContext::shader_draw_parameters_support = false;
+bool GLContext::stencil_texturing_support = false;
 bool GLContext::texture_cube_map_array_support = false;
 bool GLContext::texture_filter_anisotropic_support = false;
 bool GLContext::texture_gather_support = false;
@@ -511,6 +512,7 @@ void GLBackend::capabilities_init()
   GLContext::multi_bind_support = GLEW_ARB_multi_bind;
   GLContext::multi_draw_indirect_support = GLEW_ARB_multi_draw_indirect;
   GLContext::shader_draw_parameters_support = GLEW_ARB_shader_draw_parameters;
+  GLContext::stencil_texturing_support = GLEW_VERSION_4_3;
   GLContext::texture_cube_map_array_support = GLEW_ARB_texture_cube_map_array;
   GLContext::texture_filter_anisotropic_support = GLEW_EXT_texture_filter_anisotropic;
   GLContext::texture_gather_support = GLEW_ARB_texture_gather;

source/blender/gpu/opengl/gl_context.hh

@@ -63,6 +63,7 @@ class GLContext : public Context {
   static bool multi_bind_support;
   static bool multi_draw_indirect_support;
   static bool shader_draw_parameters_support;
+  static bool stencil_texturing_support;
   static bool texture_cube_map_array_support;
   static bool texture_filter_anisotropic_support;
   static bool texture_gather_support;

source/blender/gpu/opengl/gl_texture.cc

@@ -453,6 +453,19 @@ void GLTexture::swizzle_set(const char swizzle[4])
   }
 }
 
+void GLTexture::stencil_texture_mode_set(bool use_stencil)
+{
+  BLI_assert(GLContext::stencil_texturing_support);
+  GLint value = use_stencil ? GL_STENCIL_INDEX : GL_DEPTH_COMPONENT;
+  if (GLContext::direct_state_access_support) {
+    glTextureParameteri(tex_id_, GL_DEPTH_STENCIL_TEXTURE_MODE, value);
+  }
+  else {
+    GLContext::state_manager_active_get()->texture_bind_temp(this);
+    glTexParameteri(target_, GL_DEPTH_STENCIL_TEXTURE_MODE, value);
+  }
+}
+
 void GLTexture::mip_range_set(int min, int max)
 {
   BLI_assert(min <= max && min >= 0 && max <= mipmaps_);

source/blender/gpu/opengl/gl_texture.hh

@@ -57,6 +57,7 @@ class GLTexture : public Texture {
   void copy_to(Texture *dst) override;
   void clear(eGPUDataFormat format, const void *data) override;
   void swizzle_set(const char swizzle_mask[4]) override;
+  void stencil_texture_mode_set(bool use_stencil) override;
   void mip_range_set(int min, int max) override;
   void *read(int mip, eGPUDataFormat type) override;