[Metal] Fix missing baseInstance while still supporting older version…

…s of Metal (fixes #130).

The baseInstance versions of drawPrimitives and drawIndexedPrimitives in Metal are only supported in iOS 9.0 or later,
while the other versions are supported since iOS 8.0 and later.
If a non-zero value of baseInstance is specified, we have to use those draw functions regardless of the instanceCount value.

sources/Renderer/Metal/Command/MTCommandExecutor.mm

@@ -304,10 +304,12 @@
  else
  {
  id<MTLRenderCommandEncoder> renderEncoder = context.FlushAndGetRenderEncoder();
- if (cmd->instanceCount != 1)
+ const bool hasBaseInstance = (cmd->baseInstance != 0);
+ if (cmd->instanceCount != 1 || hasBaseInstance)
  {
- if (cmd->baseInstance != 0)
+ if (hasBaseInstance)
  {
+ /* Suppored since iOS 9.0 */
  [renderEncoder
  drawPrimitives: context.GetPrimitiveType()
  vertexStart: cmd->vertexStart
@@ -318,6 +320,7 @@
  }
  else
  {
+ /* Suppored since iOS 8.0 */
  [renderEncoder
  drawPrimitives: context.GetPrimitiveType()
  vertexStart: cmd->vertexStart
@@ -328,6 +331,7 @@
  }
  else
  {
+ /* Suppored since iOS 8.0 */
  [renderEncoder
  drawPrimitives: context.GetPrimitiveType()
  vertexStart: cmd->vertexStart
@@ -362,10 +366,12 @@
  else
  {
  id<MTLRenderCommandEncoder> renderEncoder = context.FlushAndGetRenderEncoder();
- if (cmd->instanceCount != 1)
+ const bool hasBaseVertexOrInstance = (cmd->baseVertex != 0 || cmd->baseInstance != 0);
+ if (cmd->instanceCount != 1 || hasBaseVertexOrInstance)
  {
- if (cmd->baseVertex != 0 || cmd->baseInstance != 0)
+ if (hasBaseVertexOrInstance)
  {
+ /* Suppored since iOS 9.0 */
  [renderEncoder
  drawIndexedPrimitives: context.GetPrimitiveType()
  indexCount: cmd->indexCount
@@ -379,6 +385,7 @@
  }
  else
  {
+ /* Suppored since iOS 8.0 */
  [renderEncoder
  drawIndexedPrimitives: context.GetPrimitiveType()
  indexCount: cmd->indexCount
@@ -391,6 +398,7 @@
  }
  else
  {
+ /* Suppored since iOS 8.0 */
  [renderEncoder
  drawIndexedPrimitives: context.GetPrimitiveType()
  indexCount: cmd->indexCount