Merge branch 'examples_refactor2' into viewport (#1870)

# Conflicts:
#	examples/README.txt
#	examples/directx11_example/main.cpp
#	examples/directx12_example/main.cpp
#	examples/imgui_impl_dx10.cpp
#	examples/imgui_impl_dx11.cpp
#	examples/imgui_impl_dx12.cpp
#	examples/imgui_impl_glfw.cpp
#	examples/imgui_impl_opengl2.cpp
#	examples/imgui_impl_opengl2.h
#	examples/imgui_impl_opengl3.cpp
#	examples/imgui_impl_sdl2.cpp
#	examples/imgui_impl_sdl2.h
#	examples/imgui_impl_vulkan.cpp
#	examples/imgui_impl_vulkan.h
#	examples/imgui_impl_win32.cpp
#	examples/imgui_impl_win32.h
#	examples/opengl2_example/main.cpp
#	examples/opengl3_example/main.cpp
#	examples/sdl_opengl2_example/main.cpp
#	examples/sdl_opengl3_example/main.cpp
#	examples/sdl_vulkan_example/main.cpp
#	examples/vulkan_example/main.cpp
#	imgui.cpp
#	imgui.h

imgui.h

@@ -1547,7 +1547,7 @@ typedef void (*ImDrawCallback)(const ImDrawList* parent_list, const ImDrawCmd* c
 struct ImDrawCmd
 {
     unsigned int    ElemCount;              // Number of indices (multiple of 3) to be rendered as triangles. Vertices are stored in the callee ImDrawList's vtx_buffer[] array, indices in idx_buffer[].
-    ImVec4          ClipRect;               // Clipping rectangle (x1, y1, x2, y2)
+    ImVec4          ClipRect;               // Clipping rectangle (x1, y1, x2, y2). Subtract ImDrawData->DisplayPos to get clipping rectangle in "viewport" coordinates
     ImTextureID     TextureId;              // User-provided texture ID. Set by user in ImfontAtlas::SetTexID() for fonts or passed to Image*() functions. Ignore if never using images or multiple fonts atlas.
     ImDrawCallback  UserCallback;           // If != NULL, call the function instead of rendering the vertices. clip_rect and texture_id will be set normally.
     void*           UserCallbackData;       // The draw callback code can access this.
@@ -1708,7 +1708,7 @@ struct ImDrawData
     int             CmdListsCount;          // Number of ImDrawList* to render
     int             TotalIdxCount;          // For convenience, sum of all ImDrawList's IdxBuffer.Size
     int             TotalVtxCount;          // For convenience, sum of all ImDrawList's VtxBuffer.Size
-    ImVec2          DisplayPos;             // Virtual upper-left position of the viewport to render (== ImVec2(0,0) for the main viewport == upper-left of the orthogonal projection matrix to use)
+    ImVec2          DisplayPos;             // Upper-left position of the viewport to render (== upper-left of the orthogonal projection matrix to use)
     ImVec2          DisplaySize;            // Size of the viewport to render (== io.DisplaySize for the main viewport) (DisplayPos + DisplaySize == lower-right of the orthogonal projection matrix to use)
 
     // Functions