Add pakced depth stencil to GLFWView and HeadlessView

include/mbgl/platform/gl.hpp

@@ -130,9 +130,11 @@ extern PFNGLDELETEVERTEXARRAYSPROC DeleteVertexArrays;
 extern PFNGLGENVERTEXARRAYSPROC GenVertexArrays;
 extern PFNGLISVERTEXARRAYPROC IsVertexArray;
 
+// GL_EXT_packed_depth_stencil / GL_OES_packed_depth_stencil
 extern bool isPackedDepthStencilSupported;
 #define GL_DEPTH24_STENCIL8 0x88F0
 
+// GL_OES_depth24
 extern bool isDepth24Supported;
 #define GL_DEPTH_COMPONENT24 0x81A6
 

platform/default/glfw_view.cpp

@@ -152,6 +152,10 @@ void GLFWView::initialize(mbgl::Map *map_) {
             assert(gl::ProgramBinary != nullptr);
             assert(gl::ProgramParameteri != nullptr);
         }
+
+        // Require packed depth stencil
+        gl::isPackedDepthStencilSupported = true;
+        gl::isDepth24Supported = true;
     }
 
     glfwMakeContextCurrent(nullptr);

platform/default/headless_view.cpp

@@ -85,6 +85,11 @@ void HeadlessView::loadExtensions() {
         gl::IsVertexArray = (gl::PFNGLISVERTEXARRAYPROC)glXGetProcAddress((const GLubyte *)"glIsVertexArrayARB");
     }
 #endif
+
+    // HeadlessView requires packed depth stencil
+    gl::isPackedDepthStencilSupported = true;
+    gl::isDepth24Supported = true;
+
     make_inactive();
 }