feat(doc/journal): Add dev notes about iidx HD era upscaling feature

doc/dev/journal/2023-04-13-iidx-24-gfx-upscaling.md

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+# IIDX 24 GFX upscaling notes
+
+Date: 2023-04-15
+Author: icex2
+
+Notes about my work on fixing the upscaling/downscaling feature of bemanitools for IIDX 20 to 26.
+I realized that the render backend changed significantly that the old method that worked fine
+doesn't work anymore.
+
+The tool used in the screenshots is [apitrace](https://github.com/apitrace/apitrace).
+
+## IIDX 24
+
+The GFX engine in IIDX from 20 to 26 has a changed render loop that includes built-in scaling to
+implement the SD and HD/HD* screen settings that are selectable in the operator menu
+
+### Frame 0 - GFX init part
+
+Setting up the context and device, as well as the frame buffer. This also creates the intermediate
+texture that is configured as the render target once it begins drawing the scene.
+
+![](2023-04-13-iidx-24-gfx-upscaling/init.png)
+
+### Frame 1 - A clean main render path
+
+Start the scene and set the render target to the intermediate texture.
+
+![](2023-04-13-iidx-24-gfx-upscaling/beginscene.png)
+
+After done drawing the scene, the intermediate texture is blended to the framebuffer. With a target
+2D plane having the size of the target resolution, the blending applies linear scaling to either
+up- or downscale the final image.
+
+![](2023-04-13-iidx-24-gfx-upscaling/scaling.png)
+
+## IIDX 10
+
+A recap of the old stuff, see also [my previous notes](2019-10-07-iidx-gfx-rendering-loops.md),
+as I had to look at everything again to properly understand the differences.
+
+### Frame 0 - GFX init part
+
+Setting up the context and device, as well as the frame buffer. Renders directly to the frame
+buffer.
+
+![](2023-04-13-iidx-24-gfx-upscaling/init10.png)
+
+### Frame 1 - A clean main render path
+
+Beginning the scene excerpt. The viewport needs to match the target resolution to display the
+final image correctly.
+
+![](2023-04-13-iidx-24-gfx-upscaling/beginscene10.png)
+
+Ending the scene excerpt, nothing fancy here, just swapping the back buffer.
+
+![](2023-04-13-iidx-24-gfx-upscaling/endscene10.png)