In this series of articles I’m going to show how to create some high-impact, low-effort tools to help develop your game in UE4. Tools range from simple batch files or humble debug commands to complex ensembles like the UE4 level editor or Max/Maya; but for now let’s focus on some approaches that don’t require a broad knowledge of Unreal Engine or Slate to pull off. Some of these topics deserve a post of their own, but I’m going to start with more of a survey approach and see what people are most interested in digging into.
Programming is all about strategic laziness: the guiding philosophy developing tools is to spend time now to save someone time later, improving overall developer efficiency. This might play out by allowing the user to finish the same tasks in less time or it might allow them to perform more iterations in the same amount of time, increasing polish level and fun factor. Ideally you also save more time than was involved in making the tool, but that is not a hard requirement due to other factors like user morale, making it possible for a different group of people to do the work, reducing mistakes when the cost of failure is high, etc… This is especially true when it comes to automating key processes where a mistake might cause downtime or otherwise hurt your customers, e.g., releasing a broken update or corrupting a database.
I spent some time last weekend prepping for #cgajam by playing around with different materials / effects to constrain a UE4 game to CGA colors, and came up with a drop-in post processing BP.
Download the template (requires Unreal Engine 4.16, licensed as CC0) and unzip it. You can either open the project directly and migrate the Content/CGAJam folder into your project or drop the whole folder into the templates directory of your 4.16 installation (e.g., C:\Program Files (x86)\Epic Games\UE_4.16\Templates) and then create a new project (info on how to make a project into a template here).
There’s an example map but all of the magic is wrapped up in BP_CGAPostProcess; just drop one into your level and try playing around with the settings to suit your content. You can pick one of the two palettes, adjust how much color-space dithering and screen space dithering there is, and tweak the overall gamma / brightness. For the hand painted environment I found 50% screen dither + 50% LUT dither at level 3 to give me the best results, but for the example scene with solid shapes and color fills, 100% screen dither with no LUT dither looked better.
Implementation details
CGA had a variety of different modes and palettes, but the most memorable for gaming was the 320×200 graphics mode using either palette 0 (black, red, green, yellow) or palette 1 (black, magenta, cyan, white). Color 0 (black) is actually adjustable to any of the 16 CGA colors, though it doesn’t appear to be allowed for #cgajam. The red and green components of colors 1..3 are the same in both palettes as well, only the blue color differs.
UE4 has a lookup-table texture (LUT) based color grading system, but there’s no way to control the filtering used to sample it, so it can’t produce ‘crisp’ CGA colors. It’s still useful to get colors to nearly the right place though. I’ve included 4 LUT textures for each palette with varying color-space dithering (0%, 25%, 50%, 75%); you can adjust the strength of the color grading as well to vary the effect.
Color grading LUTs for palette 0
The post-process material (M_ForceCGA_PostProcess) has a screen-space dither pattern which dims based on brightness prior to matching to one of the four colors in the active palette. The color matching (MF_ForceToCGA) and dithering (MF_DitherBrightness) are split up into separate material functions to make them easier to reuse, e.g., in the UI material.
The actual color matching is done using a cheap lookup texture with red->U and green->V (the 2×2 texture is set to uncompressed, clamped instead of wrapped uvs, nearest filtering, etc… to give us a clean and exact output value). We can ignore the input blue entirely as mentioned above, and multiply the output blue with the correct value for the current palette (dim it for palette 0 and keep it as-is for palette 1).
MF_ForceToCGAMF_DitherBrightness
User Interface
For the UI, you’ve got two options:
Stick with the CGA colors, which need to be specified differently in the UI than in the world since UI happens in a different color space, e.g., yellow is (1,1,0.092) instead of (1,1,0.333) (the correct final color will show up in the hex sRGB setting of the color picker).
Get in the right ballpark and use a retainer box with the Effect Material set to MI_ForceCGA_UI_Palette0 or MI_ForceCGA_UI_Palette1 to guarantee that you only use the correct 4 colors (recommended approach).
Using a retainer box
Avoiding flickering artifacts
There are a couple of steps in the default UE4 post-processing chain that introduce temporal artifacts in order to improve overall image quality when doing realistic rendering. These steps become very noticeable and objectionable when you do something like threshold down to 4 colors, so the example project disables them (setting r.Tonemapper.GrainQuantization to 0 and disabling post-process Anti-aliasing entirely, though you could also switch from temporal AA to FXAA instead). The DefaultEngine.ini changes to do this won’t transfer over if you just migrate the content from one project to another, so you may need to paste in:
Want a lower resolution that is a bit more like true CGA 320×200? Adjust the Screen Percentage on the post process component and set r.upscale.quality to 0 (nearest filtering) in the [SystemSettings] section of DefaultEngine.ini
Ideas for further improvement
Try combining it with an edge detection material (either on depth or on custom stencil if you want to limit the effect to foreground objects) to put black outlines around things.
Try other spatial variation patterns besides a 2×2 checkerboard; techniques like Real-time hatching would probably work quite well.
Credits
The map used in the example shots is from the “Hand Painted Environment” marketplace pack by Evgeniya Yaremko.
The Epic Games Launcher shows a thumbnail for each project, looking in two places: first in the root folder of the game for [ProjectName].png (next to the .uproject) and then Saved\AutoScreenshot.png, which is created by the editor automatically. You can create your own thumbnail (192×192 .png) and set it using the “Project Thumbnail” option in the Description category of Project Settings.
You can also customize the splash screen shown when the editor or game is starting up (separately for editor vs game, windows vs mac) in the Windows / Mac categories (under Platform) of Project Settings. The splash screens need to be .bmp (not .png), but they can be whatever size you want within reason (the startup text and project name are overlaid on top of it, so you’ll probably want to leave space for that).
You can pick application icons and mobile startup screens in the various platform settings options pages as well (the rules for these are varied and some platforms require a wide range of sizes, but it’s all listed in the corresponding settings pages and platform vendor web sites). Due to the variety of required splash screens for a universal iOS app, the size can start to add up noticeably, so it can be worthwhile to approach them differently, using large fill areas that will compress well, run pngcrush on them, etc….
