View Issue Details

Jump to NotesJump to History
IDProjectCategoryView StatusDate SubmittedLast Update
0010185ardourdocumentationpublic2026-02-14 13:492026-02-17 06:56
Reporteru1f992 Assigned To 
PrioritynormalSeverityminorReproducibilityalways
Status newResolutionopen 
PlatformUbuntuOSLinuxOS Version(any)
Product Version9.0 
Summary0010185: Cairo patch not linked from documentation
DescriptionCurrent Build-time Ardour Dependencies (https://ardour.org/current_dependencies.html) lists cairo under "Libraries Requiring Modified Versions", but I could not find the actual patch. The nightly build dependencies page (https://nightly.ardour.org/list.php#build_deps) links to the unmodified upstream cairo (`http://cairographics.org/releases/cairo-1.16.0.tar.xz`), and neither page links to a patch or patched tarball for cairo.

The freetype section of `current_dependencies.html` links directly to its patch at `https://raw.github.com/Ardour/ardour/2.0-ongoing/tools/misc-patches/freetype-bytecode.patch`. I found a file `tools/misc-patches/cairo-gradients.patch` on the same branch (commit `990fd441d9`) and it seems to produce a matching `libcairo.so.2`, but since it is not referenced from any documentation I am not sure this is the right one.

Could a link to the cairo patch be added to `current_dependencies.html` (similar to the freetype patch), or could a patched tarball be hosted on the nightly page?
Steps To Reproduce1. Visit https://ardour.org/current_dependencies.html. Cairo is listed under "Libraries Requiring Modified Versions" but has no link to a patch (compare with the Freetype section which links directly to its patch).
2. Visit https://nightly.ardour.org/list.php#build_deps. The cairo entry links to unmodified upstream source.
3. Extract `libcairo.so.2` from the Ardour 9.0 Linux x86_64 installer and compare with one built from the upstream source. The installer version contains `FORCE_BUGGY_GRADIENTS` in `.rodata` and a `getenv("ARDOUR_FORCE_BUGGY_GRADIENTS")` call in `.text` that are absent from the upstream build.
Additional InformationThe patch appears to add a `FORCE_BUGGY_GRADIENTS` environment variable check to `src/cairo-xlib-display.c` and define `CAIRO_SUPPORTS_FORCE_BUGGY_GRADIENTS_ENVIRONMENT_VARIABLE` in `src/cairo.h`. These are referenced by Ardour's `gtk2_ardour/ui_config.cc` and `gtk2_ardour/rc_option_editor.cc` via `#ifdef` guards.

Cairo is licensed under LGPL 2.1.
TagsNo tags attached.

Activities

u1f992

2026-02-16 16:14

reporter   ~0029886

I did some additional investigation and found that the patch on the 2.0-ongoing branch (tools/misc-patches/cairo-gradients.patch, commit 990fd441d9) is outdated and insufficient for the current cairo (1.16.0), unlike the freetype patch which still applies cleanly.

Two issues:

1. The original patch targets cairo 1.10.2 code that has been significantly rewritten in 1.16.0. That said, the specific `#if RENDER_MAJOR` / `display->buggy_gradients = FALSE;` block still exists at line 266, so this hunk does apply. The surrounding vendor-detection code (lines 318-343) is new in 1.16.0 but does not conflict.

2. The repository patch only modifies cairo-xlib-display.c. It does not add `#define CAIRO_SUPPORTS_FORCE_BUGGY_GRADIENTS_ENVIRONMENT_VARIABLE` to cairo.h. Without this define, Ardour's #ifdef guards in gtk2_ardour/ui_config.cc:232 and gtk2_ardour/rc_option_editor.cc:3186 compile out the entire feature. The "Possibly improve slow graphical performance" preference option never appears, and the FORCE_BUGGY_GRADIENTS environment variable is never set.

The attached patch addresses both points and produces a libcairo.so.2 binary-identical to the one shipped in the official Ardour 9.0 Linux installer.
cairo-force-buggy-gradients.patch (1,155 bytes)    
Ardour-specific patch for cairo 1.16.0: FORCE_BUGGY_GRADIENTS environment variable.

Allows users to force software gradient rendering on Linux systems with buggy
GPU drivers (notably older NVIDIA) by setting FORCE_BUGGY_GRADIENTS=1.

Origin: Ardour git commit 990fd441d9 (2.0-ongoing branch, 2012-05-22)
        plus header macro addition for Ardour's #ifdef guard.
Reference: https://ardour.org/current_dependencies.html
           "patched to allow users to disable h/w gradient rendering
            on buggy Linux video drivers"

--- a/src/cairo-xlib-display.c
+++ b/src/cairo-xlib-display.c
@@ -266,7 +266,12 @@
 #if RENDER_MAJOR == 0 && RENDER_MINOR < 10
     display->buggy_gradients = TRUE;
 #else
-    display->buggy_gradients = FALSE;
+    if (getenv ("FORCE_BUGGY_GRADIENTS")) {
+        display->buggy_gradients = TRUE;
+    }
+    else {
+        display->buggy_gradients = FALSE;
+    }
 #endif
     display->buggy_pad_reflect = FALSE;
     display->buggy_repeat = FALSE;
--- a/src/cairo.h
+++ b/src/cairo.h
@@ -3179,4 +3179,6 @@

 CAIRO_END_DECLS

+#define CAIRO_SUPPORTS_FORCE_BUGGY_GRADIENTS_ENVIRONMENT_VARIABLE
+
 #endif /* CAIRO_H */
cairo-force-buggy-gradients.patch (1,155 bytes)   

paul

2026-02-16 19:03

administrator   ~0029887

There are numerous other patches that are applied as part of our dependency stack building. They are currently in a repository that does not have public access. We will consider how best to make them available.

u1f992

2026-02-17 00:15

reporter   ~0029888

Thank you for considering making the patches publicly available. That would be very helpful.

u1f992

2026-02-17 06:56

reporter   ~0029891

Does the patch set also cover GNU termcap (statically linked into `ardour9-lua` via `libreadline.a`)?
I found two differences from upstream, and reproducing both produces a byte-identical stripped binary (excluding `.note.gnu.build-id`). The build-id still differs, so the actual patches may include additional changes that are only visible before stripping:

1. `#include <unistd.h>` in `tparam.c`. Upstream calls `write()` without a prototype, causing GCC to emit `mov $0x0,%eax` before the call. The official binary lacks this instruction. The code compiles without it, so the intent is unclear, but something makes the `write()` prototype visible in your build.
2. Upstream `Makefile.in` hardcodes `CFLAGS = -g`. The official `tputs` shows a GOT relaxation pattern for non-static globals, requiring `-fPIC`. This may be a build option rather than a source patch.

Issue History

Date Modified Username Field Change
2026-02-14 13:49 u1f992 New Issue
2026-02-16 16:14 u1f992 Note Added: 0029886
2026-02-16 16:14 u1f992 File Added: cairo-force-buggy-gradients.patch
2026-02-16 19:03 paul Note Added: 0029887
2026-02-17 00:15 u1f992 Note Added: 0029888
2026-02-17 06:56 u1f992 Note Added: 0029891