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

docs/CHANGELOG.txt

@@ -69,6 +69,8 @@ Other Changes:
 - ImDrawList, ImDrawListSplitter, Columns: Fixed an issue where starting a split right after
   a callback draw command would incorrectly override the callback draw command.
 - Misc, Freetype: Fix for rare case where FT_Get_Char_Index() succeed but FT_Load_Glyph() fails.
+- Docs: Improved and moved font documentation to docs/FONTS.md so it can be readable on the web. 
+  Updated various links/wiki accordingly. Added FAQ entry about DPI. (#2861) [@ButternCream, @ocornut] 
 - CI: Added CI test to verify we're never accidentally dragging libstdc++ (on some compiler setups,
   static constructors for non-pod data seems to drag in libstdc++ due to thread-safety concerns).
   Fixed a static contructor which led to this dependency on some compiler setups (unclear which).

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

docs/FONTS.md

@@ -14,6 +14,7 @@ In the [misc/fonts/](https://github.com/ocornut/imgui/tree/master/misc/fonts) fo
 
 ## Index
 - [Readme First](#readme-first)
+- [How should I handle DPI in my application?](#how-should-i-handle-dpi-in-my-application)
 - [Fonts Loading Instructions](#font-loading-instructions)
 - [Using Icons](#using-icons)
 - [Using FreeType Rasterizer](#using-freetype-rasterizer)
@@ -43,6 +44,13 @@ u8"こんにちは"   // this will be encoded as UTF-8
 
 ##### [Return to Index](#index)
 
+## How should I handle DPI in my application?
+
+See [FAQ entry](https://github.com/ocornut/imgui/blob/master/docs/FAQ.md#q-how-should-i-handle-dpi-in-my-application).
+
+##### [Return to Index](#index)
+
+
 ## Font Loading Instructions
 
 **Load default font:**
@@ -51,6 +59,7 @@ ImGuiIO& io = ImGui::GetIO();
 io.Fonts->AddFontDefault();
 ```
 
+
 **Load .TTF/.OTF file with:**
 ```cpp
 ImGuiIO& io = ImGui::GetIO();
@@ -58,6 +67,7 @@ io.Fonts->AddFontFromFileTTF("font.ttf", size_pixels);
 ```
 If you get an assert stating "Could not load font file!", your font filename is likely incorrect. Read "[About filenames](#about-filenames)" carefully.
 
+
 **Load multiple fonts:**
 ```cpp
 ImGuiIO& io = ImGui::GetIO();
@@ -71,6 +81,7 @@ ImGui::Text("Hello with another font");
 ImGui::PopFont();
 ```
 
+
 **For advanced options create a ImFontConfig structure and pass it to the AddFont() function (it will be copied internally):**
 ```cpp
 ImFontConfig config;
@@ -80,6 +91,7 @@ config.GlyphExtraSpacing.x = 1.0f;
 ImFont* font = io.Fonts->AddFontFromFileTTF("font.ttf", size_pixels, &config);
 ```
 
+
 **Combine multiple fonts into one:**
 ```cpp
 // Load a first font
@@ -97,6 +109,7 @@ io.Fonts->Build();
 ```
 
 **Add a fourth parameter to bake specific font ranges only:**
+
 ```cpp
 // Basic Latin, Extended Latin
 io.Fonts->AddFontFromFileTTF("font.ttf", size_pixels, NULL, io.Fonts->GetGlyphRangesDefault());
@@ -109,6 +122,27 @@ io.Fonts->AddFontFromFileTTF("font.ttf", size_pixels, NULL, io.Fonts->GetGlyphRa
 ```
 See [Using Custom Glyph Ranges](#using-custom-glyph-ranges) section to create your own ranges.
 
+
+**Example loading and using a Japanese font:**
+
+```cpp
+ImGuiIO& io = ImGui::GetIO();
+io.Fonts->AddFontFromFileTTF("NotoSansCJKjp-Medium.otf", 20.0f, NULL, io.Fonts->GetGlyphRangesJapanese());
+```
+```cpp
+ImGui::Text(u8"こんにちは！テスト %d", 123);
+if (ImGui::Button(u8"ロード"))
+{
+    // do stuff
+}
+ImGui::InputText("string", buf, IM_ARRAYSIZE(buf));
+ImGui::SliderFloat("float", &f, 0.0f, 1.0f);
+```
+
+![sample code output](https://raw.githubusercontent.com/wiki/ocornut/imgui/web/v160/code_sample_02_jp.png)
+<br>_(settings: Dark style (left), Light style (right) / Font: NotoSansCJKjp-Medium, 20px / Rounding: 5)_
+
+
 **Offset font vertically by altering the `io.Font->DisplayOffset` value:**
 ```cpp
 ImFont* font = io.Fonts->AddFontFromFileTTF("font.ttf", size_pixels);

imgui.cpp

@@ -765,11 +765,12 @@ CODE
  Q&A: Fonts, Text
  ================
 
+ Q: How should I handle DPI in my application?
  Q: How can I load a different font than the default?
  Q: How can I easily use icons in my application?
  Q: How can I load multiple fonts?
  Q: How can I display and input non-Latin characters such as Chinese, Japanese, Korean, Cyrillic?
- >> See https://www.dearimgui.org/faq (docs/FAQ.md) docs/FONTS.md
+ >> See https://www.dearimgui.org/faq and https://github.com/ocornut/imgui/edit/master/docs/FONTS.md
 
  Q&A: Concerns
  =============