On impeller, the vertices API is off by 1 pixel when using fragment shaders and textureCoordinates #151355
Description
Steps to reproduce
Given any project, in the stable channel:
- use draw vertices to paint some triangles using a
Paintobject as texture with a fragment shader. - if you specify
textureCoordinates, the bottom and right edges will be off by 1 pixel.
Expected results
To have the proper pixels painted.
Actual results
Pixels painted are removed by 1 pixel in the left and bottom edges. See screenshots and code sample below.
Code sample
Code sample
For example, given that we are painting in a canvas region of size 100x100.
If we divide the canavs region by 4 quadrants and paint the following vertices:
// Two triangles covering the top left quadrant of the region
final vertices1 = Float32List.fromList([
0.0, 0.0,
50.0, 0.0,
50.0, 50.0,
0.0, 0.0,
0.0, 50.0,
50.0, 50.0,
]);
canvas.drawVertices(
Vertices.raw(
VertexMode.triangles,
vertices1,
textureCoordinates: Float32List.fromList(vertices1),
),
BlendMode.srcOver,
Paint()..shader = shader, // any fragment shader
);
// Two triangles covering the top right quadrant of the region
final vertices2 = Float32List.fromList([
50.0, 0.0,
100.0, 0.0,
100.0, 50.0,
50.0, 0.0,
50.0, 50.0,
100.0, 50.0,
]);
canvas.drawVertices(
Vertices.raw(
VertexMode.triangles,
vertices2,
textureCoordinates: Float32List.fromList(vertices2),
),
BlendMode.srcOver,
Paint()..shader = shader, // any fragment shader
);
// Two triangles covering the bottom left quadrant of the region
final vertices3 = Float32List.fromList([
0.0, 50.0,
50.0 50.0,
50.0, 100.0,
0.0, 50.0,
0.0, 100.0,
50.0, 100.0,
]);
canvas.drawVertices(
Vertices.raw(
VertexMode.triangles,
vertices3,
textureCoordinates: Float32List.fromList(vertices3),
),
BlendMode.srcOver,
Paint()..shader = shader, // any fragment shader
);
// Two triangles covering the bottom right quadrant of the region
final vertices4 = Float32List.fromList([
50.0, 50.0,
100.0, 50.0,
100.0, 100.0,
50.0, 50.0,
50.0, 100.0,
100.0, 100.0,
]);
canvas.drawVertices(
Vertices.raw(
VertexMode.triangles,
vertices4,
textureCoordinates: Float32List.fromList(vertices4),
),
BlendMode.srcOver,
Paint()..shader = shader, // any fragment shader
);
Reproducible sample
Ive created a reproducible sample here: https://github.com/renancaraujo/impeller_drawvertices_issue
Screenshots or Video
Screenshots / Video demonstration (impeller)
The gaps observed when running with impeller on macos with pixel ratio of 1:
Screenshots / Video demonstration (skia)
The gap is not observed when running with skia in the same environment:
Logs
Logs
Logs are irrelevant
Flutter Doctor output
Doctor output
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.22.2, on macOS 14.5 23F79 darwin-arm64,
locale en-REDACTED)
[✓] Android toolchain - develop for Android devices (Android SDK version
34.0.0)
[✓] Xcode - develop for iOS and macOS (Xcode 16.0)
[✓] Chrome - develop for the web
[✓] Android Studio (version REDACTED)
[✓] VS Code (version REDACTED)
[✓] Connected device (4 available)
[✓] Network resourcesMetadata
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