GPU: Remove GPU_INDEX_U8

This type of indices is not natively supported on modern GPU and
gives warning on some implementation. The memory savings it
provides is also quite minimal and unlikely to be visible on
nowadays hardware.

This remove some uneeded struct members and makes primitive
restart always enabled by default. This can be broken by addons
if they are not careful enough but many other states have this
problem.

Also leverage GL_PRIMITIVE_RESTART_FIXED_INDEX if
ARB_ES3_compatibility is supported. This removes all API calls
to change restart index depending on indices length.

3 files changed, 40 insertions, 81 deletions

diff --git a/source/blender/gpu/intern/gpu_batch.c b/source/blender/gpu/intern/gpu_batch.c
index d1cfd5c337d..fb2a87fc8d1 100644
--- a/source/blender/gpu/intern/gpu_batch.c
+++ b/source/blender/gpu/intern/gpu_batch.c
@@ -545,36 +545,26 @@ void GPU_batch_uniform_mat4(GPUBatch *batch, const char *name, const float data[
   glUniformMatrix4fv(uniform->location, 1, GL_FALSE, (const float *)data);
 }
 
-static void primitive_restart_enable(const GPUIndexBuf *el)
+static void primitive_restart_index(const GPUIndexBuf *el)
 {
-  // TODO(fclem) Replace by GL_PRIMITIVE_RESTART_FIXED_INDEX when we have ogl 4.3
-  glEnable(GL_PRIMITIVE_RESTART);
-  GLuint restart_index = (GLuint)0xFFFFFFFF;
-
 #if GPU_TRACK_INDEX_RANGE
-  if (el->index_type == GPU_INDEX_U8) {
-    restart_index = (GLuint)0xFF;
-  }
-  else if (el->index_type == GPU_INDEX_U16) {
-    restart_index = (GLuint)0xFFFF;
+  /* Can be removed if GL 4.3 is available. */
+  if (!GLEW_ARB_ES3_compatibility) {
+    /* Stay sync with GPU_state_init(). */
+    static int last_type = GPU_INDEX_U32;
+    if (el->index_type != last_type) {
+      GLuint restart_index = (el->index_type == GPU_INDEX_U16) ? (GLuint)0xFFFF :
+                                                                 (GLuint)0xFFFFFFFF;
+      glPrimitiveRestartIndex(restart_index);
+    }
   }
 #endif
-
-  glPrimitiveRestartIndex(restart_index);
-}
-
-static void primitive_restart_disable(void)
-{
-  glDisable(GL_PRIMITIVE_RESTART);
 }
 
 static void *elem_offset(const GPUIndexBuf *el, int v_first)
 {
 #if GPU_TRACK_INDEX_RANGE
-  if (el->index_type == GPU_INDEX_U8) {
-    return (GLubyte *)0 + v_first;
-  }
-  else if (el->index_type == GPU_INDEX_U16) {
+  if (el->index_type == GPU_INDEX_U16) {
     return (GLushort *)0 + v_first;
   }
 #endif
@@ -641,9 +631,7 @@ void GPU_batch_draw_advanced(GPUBatch *batch, int v_first, int v_count, int i_fi
 #endif
     void *v_first_ofs = elem_offset(el, v_first);
 
-    if (el->use_prim_restart) {
-      primitive_restart_enable(el);
-    }
+    primitive_restart_index(el);
 
     if (GLEW_ARB_base_instance) {
       glDrawElementsInstancedBaseVertexBaseInstance(
@@ -653,10 +641,6 @@ void GPU_batch_draw_advanced(GPUBatch *batch, int v_first, int v_count, int i_fi
       glDrawElementsInstancedBaseVertex(
           batch->gl_prim_type, v_count, index_type, v_first_ofs, i_count, base_index);
     }
-
-    if (el->use_prim_restart) {
-      primitive_restart_disable();
-    }
   }
   else {
     if (GLEW_ARB_base_instance) {
diff --git a/source/blender/gpu/intern/gpu_draw.c b/source/blender/gpu/intern/gpu_draw.c
index 5f27a0e93cd..c3c05c39c00 100644
--- a/source/blender/gpu/intern/gpu_draw.c
+++ b/source/blender/gpu/intern/gpu_draw.c
@@ -1372,6 +1372,16 @@ void GPU_state_init(void)
   glDisable(GL_CULL_FACE);
 
   gpu_disable_multisample();
+
+  /* This is a bit dangerous since addons could change this. */
+  glEnable(GL_PRIMITIVE_RESTART);
+  glPrimitiveRestartIndex((GLuint)0xFFFFFFFF);
+
+  /* TODO: Should become default. But needs at least GL 4.3 */
+  if (GLEW_ARB_ES3_compatibility) {
+    /* Takes predecence over GL_PRIMITIVE_RESTART */
+    glEnable(GL_PRIMITIVE_RESTART_FIXED_INDEX);
+  }
 }
 
 /** \name Framebuffer color depth, for selection codes
diff --git a/source/blender/gpu/intern/gpu_element.c b/source/blender/gpu/intern/gpu_element.c
index 0b7f37af522..380de4c4e65 100644
--- a/source/blender/gpu/intern/gpu_element.c
+++ b/source/blender/gpu/intern/gpu_element.c
@@ -33,10 +33,11 @@
 
 #define KEEP_SINGLE_COPY 1
 
+#define RESTART_INDEX 0xFFFFFFFF
+
 static GLenum convert_index_type_to_gl(GPUIndexBufType type)
 {
   static const GLenum table[] = {
-      [GPU_INDEX_U8] = GL_UNSIGNED_BYTE, /* GL has this, Vulkan does not */
       [GPU_INDEX_U16] = GL_UNSIGNED_SHORT,
       [GPU_INDEX_U32] = GL_UNSIGNED_INT,
   };
@@ -47,7 +48,6 @@ uint GPU_indexbuf_size_get(const GPUIndexBuf *elem)
 {
 #if GPU_TRACK_INDEX_RANGE
   static const uint table[] = {
-      [GPU_INDEX_U8] = sizeof(GLubyte), /* GL has this, Vulkan does not */
       [GPU_INDEX_U16] = sizeof(GLushort),
       [GPU_INDEX_U32] = sizeof(GLuint),
   };
@@ -80,10 +80,8 @@ int GPU_indexbuf_primitive_len(GPUPrimType prim_type)
 void GPU_indexbuf_init_ex(GPUIndexBufBuilder *builder,
                           GPUPrimType prim_type,
                           uint index_len,
-                          uint vertex_len,
-                          bool use_prim_restart)
+                          uint vertex_len)
 {
-  builder->use_prim_restart = use_prim_restart;
   builder->max_allowed_index = vertex_len - 1;
   builder->max_index_len = index_len;
   builder->index_len = 0;  // start empty
@@ -100,7 +98,7 @@ void GPU_indexbuf_init(GPUIndexBufBuilder *builder,
 #if TRUST_NO_ONE
   assert(verts_per_prim != -1);
 #endif
-  GPU_indexbuf_init_ex(builder, prim_type, prim_len * (uint)verts_per_prim, vertex_len, false);
+  GPU_indexbuf_init_ex(builder, prim_type, prim_len * (uint)verts_per_prim, vertex_len);
 }
 
 void GPU_indexbuf_add_generic_vert(GPUIndexBufBuilder *builder, uint v)
@@ -118,9 +116,8 @@ void GPU_indexbuf_add_primitive_restart(GPUIndexBufBuilder *builder)
 #if TRUST_NO_ONE
   assert(builder->data != NULL);
   assert(builder->index_len < builder->max_index_len);
-  assert(builder->use_prim_restart);
 #endif
-  builder->data[builder->index_len++] = GPU_PRIM_RESTART;
+  builder->data[builder->index_len++] = RESTART_INDEX;
 }
 
 void GPU_indexbuf_add_point_vert(GPUIndexBufBuilder *builder, uint v)
@@ -180,7 +177,7 @@ static uint index_range(const uint values[], uint value_len, uint *min_out, uint
   uint max_value = values[0];
   for (uint i = 1; i < value_len; ++i) {
     const uint value = values[i];
-    if (value == GPU_PRIM_RESTART) {
+    if (value == RESTART_INDEX) {
       continue;
     }
     else if (value < min_value) {
@@ -195,33 +192,10 @@ static uint index_range(const uint values[], uint value_len, uint *min_out, uint
   return max_value - min_value;
 }
 
-static void squeeze_indices_byte(GPUIndexBufBuilder *builder, GPUIndexBuf *elem)
-{
-  const uint *values = builder->data;
-  const uint index_len = elem->index_len;
-
-  /* data will never be *larger* than builder->data...
-   * converting in place to avoid extra allocation */
-  GLubyte *data = (GLubyte *)builder->data;
-
-  if (elem->max_index > 0xFF) {
-    const uint base = elem->min_index;
-    elem->base_index = base;
-    elem->min_index = 0;
-    elem->max_index -= base;
-    for (uint i = 0; i < index_len; ++i) {
-      data[i] = (values[i] == GPU_PRIM_RESTART) ? 0xFF : (GLubyte)(values[i] - base);
-    }
-  }
-  else {
-    elem->base_index = 0;
-    for (uint i = 0; i < index_len; ++i) {
-      data[i] = (GLubyte)(values[i]);
-    }
-  }
-}
-
-static void squeeze_indices_short(GPUIndexBufBuilder *builder, GPUIndexBuf *elem)
+static void squeeze_indices_short(GPUIndexBufBuilder *builder,
+                                  GPUIndexBuf *elem,
+                                  uint min_index,
+                                  uint max_index)
 {
   const uint *values = builder->data;
   const uint index_len = elem->index_len;
@@ -230,13 +204,10 @@ static void squeeze_indices_short(GPUIndexBufBuilder *builder, GPUIndexBuf *elem
    * converting in place to avoid extra allocation */
   GLushort *data = (GLushort *)builder->data;
 
-  if (elem->max_index > 0xFFFF) {
-    const uint base = elem->min_index;
-    elem->base_index = base;
-    elem->min_index = 0;
-    elem->max_index -= base;
+  if (max_index > 0xFFFF) {
+    elem->base_index = min_index;
     for (uint i = 0; i < index_len; ++i) {
-      data[i] = (values[i] == GPU_PRIM_RESTART) ? 0xFFFF : (GLushort)(values[i] - base);
+      data[i] = (values[i] == RESTART_INDEX) ? 0xFFFF : (GLushort)(values[i] - min_index);
     }
   }
   else {
@@ -262,24 +233,18 @@ void GPU_indexbuf_build_in_place(GPUIndexBufBuilder *builder, GPUIndexBuf *elem)
   assert(builder->data != NULL);
 #endif
   elem->index_len = builder->index_len;
-  elem->use_prim_restart = builder->use_prim_restart;
   elem->ibo_id = 0; /* Created at first use. */
 
 #if GPU_TRACK_INDEX_RANGE
-  uint range = index_range(builder->data, builder->index_len, &elem->min_index, &elem->max_index);
+  uint min_index, max_index;
+  uint range = index_range(builder->data, builder->index_len, &min_index, &max_index);
 
   /* count the primitive restart index. */
-  if (elem->use_prim_restart) {
-    range += 1;
-  }
+  range += 1;
 
-  if (range <= 0xFF) {
-    elem->index_type = GPU_INDEX_U8;
-    squeeze_indices_byte(builder, elem);
-  }
-  else if (range <= 0xFFFF) {
+  if (range <= 0xFFFF) {
     elem->index_type = GPU_INDEX_U16;
-    squeeze_indices_short(builder, elem);
+    squeeze_indices_short(builder, elem, min_index, max_index);
   }
   else {
     elem->index_type = GPU_INDEX_U32;