## Summary of the Pull Request
- Adjusts scaling practices in `DxEngine` (and related scaling practices in `TerminalControl`) for pixel-perfect row baselines and spacing at High DPI such that differential row-by-row rendering can be applied at High DPI.
## References
- #5185
## PR Checklist
* [x] Closes#5320, closes#3515, closes#1064
* [x] I work here.
* [x] Manually tested.
* [x] No doc.
* [x] Am core contributor. Also discussed with some of them already via Teams.
## Detailed Description of the Pull Request / Additional comments
**WAS:**
- We were using implicit DPI scaling on the `ID2D1RenderTarget` and running all of our processing in DIPs (Device-Independent Pixels). That's all well and good for getting things bootstrapped quickly, but it leaves the actual scaling of the draw commands up to the discretion of the rendering target.
- When we don't get to explicitly choose exactly how many pixels tall/wide and our X/Y placement perfectly, the nature of floating point multiplication and division required to do the presentation can cause us to drift off slightly out of our control depending on what the final display resolution actually is.
- Differential drawing cannot work unless we can know the exact integer pixels that need to be copied/moved/preserved/replaced between frames to give to the `IDXGISwapChain1::Present1` method. If things spill into fractional pixels or the sizes of rows/columns vary as they are rounded up and down implicitly, then we cannot do the differential rendering.
**NOW:**
- When deciding on a font, the `DxEngine` will take the scale factor into account and adjust the proposed height of the requested font. Then the remainder of the existing code that adjusts the baseline and integer-ifies each character cell will run naturally from there. That code already works correctly to align the height at normal DPI and scale out the font heights and advances to take an exact integer of pixels.
- `TermControl` has to use the scale now, in some places, and stop scaling in other places. This has to do with how the target's nature used to be implicit and is now explicit. For instance, determining where the cursor click hits must be scaled now. And determining the pixel size of the display canvas must no longer be scaled.
- `DxEngine` will no longer attempt to scale the invalid regions per my attempts in #5185 because the cell size is scaled. So it should work the same as at 96 DPI.
- The block is removed from the `DxEngine` that was causing a full invalidate on every frame at High DPI.
- A TODO was removed from `TermControl` that was invalidating everything when the DPI changed because the underlying renderer will already do that.
## Validation Steps Performed
* [x] Check at 150% DPI. Print text, scroll text down and up, do selection.
* [x] Check at 100% DPI. Print text, scroll text down and up, do selection.
* [x] Span two different DPI monitors and drag between them.
* [x] Giant pile of tests in https://github.com/microsoft/terminal/pull/5345#issuecomment-614127648
Co-authored-by: Dustin Howett <duhowett@microsoft.com>
Co-authored-by: Mike Griese <migrie@microsoft.com>
## Summary of the Pull Request
Introduces convenience type `til::size` which automatically implements our best practices for size-related types and provides automatic conversions in/out of the relevant types.
## PR Checklist
* [x] In support of Differental Rendering #778
* [X] I work here.
* [x] Tests added/passed
* [x] I'm a core contributor.
## Detailed Description of the Pull Request / Additional comments
- Automatically converts in from anything with a X/Y (console `COORD`) or cx/cy (Win32 `SIZE`)
- Automatically converts out to `COORD`, `SIZE`, or `D2D1_SIZE_F`.
- Constructs from bare integers written into source file
- Default constructs to empty
- Uses Chromium Math for all basic math operations (+, -, *, /)
- Provides equality tests
- Adds initial proposal for division-to-ceiling (round up division) that attempts to `ceil` without any floating point math.
- Accessors for height/width
- Type converting accessors (that use safe conversions and throw) for height/width
- Convenience function for area calculation (as that's common with type) and uses safe math to do it.
- TAEF/WEX Output and Comparators so they will print very nicely with `VERIFY` and `Log` macros in our testing suite.
## Validation Steps Performed
- See automated tests of functionality.
## Summary of the Pull Request
Introduces a type that is basically an array (stack allocated, fixed size) that reports size based on how many elements are actually filled (from the front), iterates only the filled ones, and has some basic vector push/pop semantics.
## PR Checklist
* [x] I work here
* [x] I work here
* [x] I work here
* [ ] I'd love to roll this out to SomeViewports.... maybe in this commit or a follow on one.
* [ ] We need a TIL tests library and I should test this there.
## Detailed Description of the Pull Request / Additional comments
The original gist of this was used for `SomeViewports` which was a struct to hold between 0 and 4 viewports, based on how many were left after subtraction (since rectangle subtraction functions in Windows code simply fail for resultants that yield >=2 rectangle regions.)
I figured now that we're TIL-ifying useful common utility things that this would be best suited to a template because I'm certain there are other circumstances where we would like to iterate a partially filled array and want it to not auto-resize-up like a vector would.
## Validation Steps Performed
* [ ] TIL tests added
