Any custom-shader breaks rendering: error drawing err=error.OpenGLFailed every frame, blank window

[ReStranger]

Issue Description

On Ghostty tip, enabling any custom-shader — including a trivial 4-line
passthrough — breaks all rendering: the window opens but stays fully black,
and the log is spammed with one warning per frame:

warning(renderer_thread): error drawing err=error.OpenGLFailed

Without custom-shader the same setup renders fine with zero warnings.

This is not specific to a particular shader: the well-known
cursor_smear.glsl and a minimal passthrough shader fail identically, so the
whole custom-shader path (rather than a single shader) looks broken on this
setup. No shader-load warnings appear — only the per-frame draw errors —
so the shader seems to load but fail at draw time.

Renderer-specific info (per the template tips): OpenGL renderer, AMD Radeon
RX 580 (Polaris, RADV), Mesa 26.2.2, Wayland.

Checked for duplicates before filing: #9060 (error.EndOfStream at shader
load, fixed for 1.3.0), #4729 (multiple-shader chaining, fixed in 1.1.0),
discussion #8695 (Intel Mac, 1.2.0), and recent shader discussions #12504
(Debug-build crash, different symptom), #12495, #11647, #4835 — none match
(any custom shader → per-frame OpenGLFailed + blank window on
Linux/Wayland OpenGL).

Expected Behavior

Passthrough shader renders the terminal as if no shader were set; no
per-frame errors.

Actual Behavior

Blank window + error.OpenGLFailed on every frame whenever any
custom-shader is configured. A marker command (echo SHADER_TEST_MARKER_OK) printed by the child process never becomes visible;
confirmed via screenshot (window with class com.mitchellh.ghostty is
present but entirely black).

Reproduction Steps

1. custom-shader unset → launch, terminal renders normally, no warnings.
2. Use an isolated config containing only:

   custom-shader = /path/to/passthrough.glsl
   window-decoration = false
   

   (verified with an isolated XDG_CONFIG_HOME, real user config untouched;
   ghostty +validate-config is clean).
3. Launch with a visible marker, e.g.
   ghostty -e sh -c 'echo SHADER_TEST_MARKER_OK; exec zsh'
   → window opens but stays fully black, the marker text never appears.
4. Observe the log filling with warning(renderer_thread): error drawing err=error.OpenGLFailed — 250–400 entries within seconds of launch.
5. Removing custom-shader (no other change) fixes it immediately.

Same result with cursor_smear.glsl.

Ghostty Logs

warning(renderer_thread): error drawing err=error.OpenGLFailed
warning(renderer_thread): error drawing err=error.OpenGLFailed
warning(renderer_thread): error drawing err=error.OpenGLFailed
... (250-400 such lines within seconds, nothing else shader-related;
... no crash, no coredump)

Full log excerpt with context:

info: renderer=renderer.generic.Renderer(renderer.OpenGL)
warning(renderer_thread): error drawing err=error.OpenGLFailed
warning(renderer_thread): error drawing err=error.OpenGLFailed

Ghostty Version

Ghostty 1.3.2-dev+d4c88d8-nix

Version
  - version: 1.3.2-dev+d4c88d8-nix
  - channel: tip
Build Config
  - Zig version   : 0.16.0
  - build mode    : .ReleaseFast
  - app runtime   : .gtk
  - font engine   : .fontconfig_freetype
  - renderer      : renderer.generic.Renderer(renderer.OpenGL)
  - libxev        : io_uring
  - kernel version: 7.2.4-cachyos-lto
  - desktop env   : other
  - GTK version   :
    build         : 4.22.4
    runtime       : 4.22.4
  - libadwaita    : enabled
    build         : 1.9.3
    runtime       : 1.9.3
  - libX11        : enabled
  - libwayland    : enabled
(Also reproduced on the previous tip `0c2a290`. Nix build — flagging
explicitly in case nix-specific patches are suspected.)

OS Version Information

NixOS (kernel 7.2.4-cachyos-lto)

(Linux only) Display Server

Wayland

(Linux only) Desktop Environment/Window Manager

Hyprland

Minimal Ghostty Configuration

custom-shader = /path/to/passthrough.glsl
window-decoration = false

Additional Relevant Configuration

passthrough.glsl (minimal reproducing shader)

void mainImage(out vec4 fragColor, in vec2 fragCoord) {
    vec2 uv = fragCoord / iResolution.xy;
    fragColor = vec4(texture(iChannel0, uv).rgb, 1.0);
}

Also fails with cursor_smear.glsl from the ghostty-shaders collection
(same per-frame error.OpenGLFailed, blank window).

I acknowledge that:

• I have reviewed the FAQ and confirm that my issue is NOT among them.
• I have searched the Ghostty documentation and confirm there doesn't exist a configuration option that solves my issue.
• I have searched the Ghostty repository (both open and closed Discussions and Issues) and confirm this is not a duplicate of an existing issue or discussion.
• I have checked the "Preview" tab on all text fields to ensure that everything looks right, and have wrapped all configuration and code in code blocks with a group of three backticks (```) on separate lines.

[pluiedev]

Could you see if #14279 works for you?

[ReStranger]

yes