[v2,33/37] libcamera: shaders: Fix neighbouring positions in 8-bit debayering
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Message ID 20250824-b4-v0-5-2-gpuisp-v2-a-v2-33-96f4576c814e@linaro.org
State New
Headers show
Series
  • Add GLES 2.0 GPUISP to libcamera
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Commit Message

Bryan O'Donoghue Aug. 24, 2025, 12:48 a.m. UTC 
From: Milan Zamazal <mzamazal@redhat.com>

When accessing a texture position in a shader, the pixel with the
nearest centre to the specified texture coordinates (as mandated by
specifying GL_NEAREST parameter) is taken.  The current vertex shader
determines the positions of the neighbouring pixels by adding the
provided texture steps to the exact centre pixel coordinates.  But this
places the computed coordinates, from the point of view of GL_NEAREST,
exactly between the pixels and is thus prone to floating point
inaccuracies.  Wrong neighbouring pixel coordinates may be used,
resulting in artefacts in the output image.

Let's fix the problem by shifting the initial coordinates a bit from the
pixel border.

Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
---
 include/libcamera/internal/shaders/bayer_8.vert | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Patch
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diff --git a/include/libcamera/internal/shaders/bayer_8.vert b/include/libcamera/internal/shaders/bayer_8.vert
index fb5109eee3f556e4f4e4e444899eff8d922be573..fc1cf89f2d98acf8ebc4501cadad194fd07985bd 100644
--- a/include/libcamera/internal/shaders/bayer_8.vert
+++ b/include/libcamera/internal/shaders/bayer_8.vert
@@ -44,10 +44,10 @@  void main(void) {
     center.xy = textureIn;
     center.zw = textureIn * tex_size + tex_bayer_first_red;
 
-    xCoord = center.x + vec4(-2.0 * tex_step.x,
-                             -tex_step.x, tex_step.x, 2.0 * tex_step.x);
-    yCoord = center.y + vec4(-2.0 * tex_step.y,
-                              -tex_step.y, tex_step.y, 2.0 * tex_step.y);
+    xCoord = center.x + 0.1 * tex_step.x +
+      vec4(-2.0 * tex_step.x, -tex_step.x, tex_step.x, 2.0 * tex_step.x);
+    yCoord = center.y + 0.1 * tex_step.y +
+      vec4(-2.0 * tex_step.y, -tex_step.y, tex_step.y, 2.0 * tex_step.y);
 
     gl_Position = proj_matrix * vertexIn;
 }