I built two handheld LCD shaders for RetroArch: one for the original Game Boy and one for the backlit GBA SP AGS-101.
The goal is not to add another filter that merely feels retro. It is to rebuild how those two displays produced an image, starting from real measurements, period research, and the way each panel was driven.
The short version is: measure first, then calculate.
Many handheld shaders begin with an imagined “old LCD” color and blend a few previous frames to create ghosting.
That can create a nostalgic mood, but it can also go in very different directions. Some original Game Boy shaders become extremely bright green. Others look more like a generic calculator LCD than the display in an actual Game Boy.
Both may look old, but neither is necessarily faithful to a particular panel. They often reproduce what someone remembers an old screen looking like, not how that screen actually behaved.
Both images below were captured with the current Game Boy shader enabled. This is not an on/off comparison. Before getting into the model, take a look at the color, texture, crosstalk, and motion trail and decide whether they resemble the original Game Boy you remember. The sections below explain why those details were not tuned from memory.
| Title screen — crosstalk | Falling piece — ghosting |
|---|---|
 |
 |
The broad, high-contrast title graphics expose interaction between rows and columns. The falling piece in the second image leaves a vertical trail that makes the LCD response visible. Neither effect is blur painted over the final image; both come from display state that continues to evolve over time.
If the goal is to reproduce a particular screen, the first step is not opening a color picker. It is finding out what the screen actually displayed.
Retro Display Lab uses real measurements and color-managed references to reconstruct panel color, gray levels, and black/white anchors, then maps the result correctly to standard sRGB. The original Game Boy is not simply “four greens”: its four game-controlled shades sit alongside a separate optical background for the undriven LCD. The AGS-101 likewise has its own black level, gray relationship, and native color behavior; lowering saturation is not a substitute for measuring them.
Here, “color calibrated” means that the shader output is mapped to sRGB from measurement data. On a properly calibrated viewing display, the result can approach the original-panel color reconstructed by the model. A shader cannot automatically correct a modern display that is itself badly miscalibrated.
A real LCD does not produce ghosting by blending several complete frames. Think of each liquid-crystal pixel as a tiny window blind: after its electrical signal changes, it needs time to move, and a light-to-dark transition does not necessarily follow the same path as a dark-to-light transition.
The game’s color codes are therefore converted into simulated panel drive. An algorithm built from physical models then calculates how every virtual liquid-crystal pixel changes. Each pixel retains its previous state; the next state depends on drive, material behavior, scan position, and display history.
This is not a physical reconstruction of a panel. It is an algorithm that makes the panel’s physical principles run in real time on a GPU. Ghosting, crosstalk, and image retention are outputs of that model rather than effects pasted on at the end.
models/nintendo-dmg-01 reconstructs the original
Game Boy’s reflective passive-matrix STN LCD:
- four game-controlled shades plus a distinct undriven optical background;
- exact Game Boy scan timing, effective electrical drive, STN response, and reflected optical output;
- row/column electrode loading and local crosstalk instead of generic spatial blur;
- asymmetric gray transitions and slow, per-pixel ionic image retention;
- rectangular pixel apertures, undriven gaps, and reflector shadow;
- reference, heavy-ghosting, aged-unit, and accelerated-experiment presets.
The DMG-01 evidence map records how each
source enters the code and separates direct data from literature-constrained
reconstruction. Machine-readable decisions and implementation history live in
reconstruction-v1.json
and the implementation to-do.
The later GBA SP AGS-101 uses a backlit TFT LCD, not the same display technology as the original Game Boy. It responds faster, but different color and brightness transitions still take different paths. Scan timing, drive state, and the BGR subpixel arrangement also affect the final image.
I therefore did not reuse the Game Boy ghosting effect. The AGS-101 has its own color, electrical, temporal-response, and pixel-structure model.
| Shader off — raw emulator output | Shader on — AGS-101 model |
|---|---|
 |
 |
The difference is not just saturation or brightness. The model combines a measured 32-code color response and black/white anchors, continuous per-subpixel TFT gray-to-gray state, alternating drive and slow residual-DC retention, GBA scan/latch/optical-onset timing, and the final BGR pixel aperture.
No complete gray-to-gray matrix or motherboard timing trace has yet been recovered for the referenced AGS-101. The default therefore uses documented analytic models and candidates constrained by period literature. A deterministic measured-table path remains ready for better transition data. See the AGS-101 evidence map for the exact classifications and limits.
The project uses the available panel measurements, color-managed original-display references, drive information, and timing evidence for the Game Boy and AGS-101, together with research on comparable panels and liquid-crystal materials from the same era.
When complete original data is unavailable, period-appropriate literature is used to bound a reasonable range. Candidate values and uncertainty are published instead of presenting a derived number as a direct panel measurement.
The most accurate description is a physical-model-based reconstruction constrained by measurement and literature. The full rules are in the methodology, reference policy, and reference index.
Every image in this README was rendered in RetroArch on a KONKR Pocket Advance (GT78-VN) and captured directly from its 960×640 framebuffer:
- GBA content maps 240×160 to 960×640 at an exact 4× scale;
- Game Boy content maps 160×144 to a 640×576 viewport at an exact 4× scale, with a bezel around it.
These are direct captures of the handheld GPU output, not photographs of the physical panel. The KONKR target is currently labeled sRGB-neutral and unmeasured; that is not the same as an instrument-calibrated sRGB display.
Game imagery is used only to demonstrate shader behavior. Tetris, Mario, Nintendo trademarks, and game content belong to their respective owners.
- Stable v0.5.0: fixed tag ZIP
- Release notes: GitHub Releases
- Latest development snapshot:
mainas ZIP - Git:
git clone https://github.com/JohnnySun/retro-display-lab.git
- Extract or clone the project into
RetroArch/shaders/retro-display-lab. - Switch to the Vulkan video driver; enable integer scaling when the target profile requires it.
- Disable the emulator core’s own frame mixing, or temporal response will be calculated twice.
- Load the target profile
.slangpthat matches your device.
For the tested KONKR GT78-VN target, use:
retro-display-lab/targets/konkr-gt78-vn/960x640-srgb-neutral/presets/dmg01-reference-v1.slangp
For GBA content on the same device, use:
retro-display-lab/targets/konkr-gt78-vn/960x640-srgb-neutral/presets/ags101-physics-seed-v1.slangp
For another display, start from the model preset and build a separate target profile. Do not treat KONKR-specific compensation as a property of the original Game Boy or AGS-101 panel. See the installation guide for the complete procedure.
npm testThe test suite checks shader and preset structure, deterministic generated assets, reference IDs, shade order, the STN surrogate, crosstalk, TFT gray-to-gray behavior, residual DC, scan causality, target scale, HCS color vectors, and honest labeling of unmeasured targets.
Before submitting a PR, read the reference policy
and contribution guide. For academic or technical use, cite
CITATION.cff and the model-local references behind the
mechanisms you used.
Original code and documentation are Apache-2.0. Third-party sources keep their own terms; this repository does not redistribute BGB images, commercial ROMs, or unlicensed HCS shader/data files.