Added FAQ entry about DPI. Added Japanese font loading example.

docs/FAQ.md

@@ -27,6 +27,7 @@ or view this file with any Markdown viewer.
 | [How can I interact with standard C++ types (such as std::string and std::vector)?](#q-how-can-i-interact-with-standard-c-types-such-as-stdstring-and-stdvector) |
 | [How can I display custom shapes? (using low-level ImDrawList API)](#q-how-can-i-display-custom-shapes-using-low-level-imdrawlist-api) |
 | **Q&A: Fonts, Text** |
+| [How should I handle DPi in my application?](#q-how-should-i-handle-dpi-in-my-application) |
 | [How can I load a different font than the default?](#q-how-can-i-load-a-different-font-than-the-default) |
 | [How can I easily use icons in my application?](#q-how-can-i-easily-use-icons-in-my-application) |
 | [How can I load multiple fonts?](#q-how-can-i-load-multiple-fonts) |
@@ -441,10 +442,33 @@ ImGui::End();
 
 # Q&A: Fonts, Text
 
+### Q: How should I handle DPI in my application?
+
+The short answer is: obtain the desired DPI scale, load a suitable font resized with that scale (always round down font size to nearest integer), and scale your Style structure accordingly using `style.ScaleAllSizes()`. 
+
+Your application may want to detect DPI change and reload the font and reset style being frames.
+
+Your ui code  should avoid using hardcoded constants for size and positioning. Prefer to express values as multiple of reference values such as `ImGui::GetFontSize()` or `ImGui::GetFrameHeight()`. So e.g. instead of seeing a hardcoded height of 500 for a given item/window, you may want to use `30*ImGui::GetFontSize()` instead.
+
+Down the line Dear ImGui will provide a variety of standardized reference values to facilitate using this.
+
+Applications in the `examples/` folder are not DPI aware partly because they are unable to load a custom font from the file-system (may change that in the future).
+
+The reason DPI is not auto-magically solved in stock examples is that we don't yet have a satisfying solution for the "multi-dpi"  problem (using the `docking` branch: when multiple viewport windows are over multiple monitors using different DPI scale). The current way to handle this on the application side is:
+- Create and maintain one font atlas per active DPI scale (e.g. by iterating `platform_io.Monitors[]` before `NewFrame()`).
+- Hook `platform_io.OnChangedViewport()` to detect when a `Begin()` call makes a Dear ImGui window change monitor (and therefore DPI).
+- In the hook: swap atlas, swap style with correctly sized one, remap the current font from one atlas to the other (may need to maintain a remapping table of your fonts at variying DPI scale).
+
+This approach is relatively easy and functional but come with two issues:
+- It's not possibly to reliably size or position a window ahead of `Begin()` without knowing on which monitor it'll land.
+- Style override may be lost during the `Begin()` call crossing monitor boundaries. You may need to do some custom scaling mumbo-jumbo if you want your `OnChangedViewport()` handler to preserve style overrides.
+
+Please note that if you are not using multi-viewports with multi-monitors using different DPI scale, you can ignore all of this and use the simpler technique recommended at the top.
+
 ### Q: How can I load a different font than the default?
 Use the font atlas to load the TTF/OTF file you want:
 
-```c
+```cpp
 ImGuiIO& io = ImGui::GetIO();
 io.Fonts->AddFontFromFileTTF("myfontfile.ttf", size_in_pixels);
 io.Fonts->GetTexDataAsRGBA32() or GetTexDataAsAlpha8()
@@ -459,7 +483,7 @@ Default is ProggyClean.ttf, monospace, rendered at size 13, embedded in dear img
 New programmers: remember that in C/C++ and most programming languages if you want to use a
 backslash \ within a string literal, you need to write it double backslash "\\":
 
-```c
+```cpp
 io.Fonts->AddFontFromFileTTF("MyFolder\MyFont.ttf", size);  // WRONG (you are escaping the M here!)
 io.Fonts->AddFontFromFileTTF("MyFolder\\MyFont.ttf", size;  // CORRECT
 io.Fonts->AddFontFromFileTTF("MyFolder/MyFont.ttf", size);  // ALSO CORRECT