| Summary: | Blurry results when scaling+copying a vector surface to an image surface | ||
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| Product: | cairo | Reporter: | Ian Britten <britten> |
| Component: | general | Assignee: | Carl Worth <cworth> |
| Status: | RESOLVED FIXED | QA Contact: | cairo-bugs mailing list <cairo-bugs> |
| Severity: | normal | ||
| Priority: | medium | ||
| Version: | 1.8.6 | ||
| Hardware: | All | ||
| OS: | All | ||
| Whiteboard: | |||
| i915 platform: | i915 features: | ||
| Attachments: |
Blurry output, from attached sample code
Sample program attempting to copy+scale PDF to Image Sample program showing workaround |
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Description
Ian Britten
2010-09-20 08:15:27 UTC
Created attachment 38814 [details]
Sample program attempting to copy+scale PDF to Image
Created attachment 38846 [details]
Sample program showing workaround
Attached is a (more extensive) sample, containing a work-around that seems to be working.
As suggested by ranma42 (IRC), performing the scaling onto a second vector/PDF surface, and then copying the PDF to the Image for rasterization (with a 1-1 scaling) almost works. The final key is to set the filtering to CAIRO_FILTER_NEAREST, when scaling the source PDF to the temporary PDF.
Admittedly, setting the filtering seems like it should be unnecessary, since it should be copying vector to vector (ie: lossless). However, that is probably the crux of the Cairo problem. Hopefully in the future version of Cairo, a 1-step copy will 'just work', and this 2-step workaround won't be needed.
Actually, after looking closer, this isn't actually working as I would have hoped/expected... It seems that what looks like a 'pixel' in the final image is much bigger than an single image pixel. In my example, the surface is scaled by 11. Unfortunately, when examining the final image, each visual 'pixel' that has been rendered is actually made up of 11x11 individual image pixels. In other words, the result is far coarser and pixelated than it should be. I wanted to create a pattern from an SVG file to be use for repeatedly
drawing, and ranm47 on #cairo warned me I might hit this problem. The
code I came up with:
RsvgHandle *handle = rsvg_handle_new_from_file(filename, &error);
cairo_surface_t *surface = cairo_svg_surface_create_for_stream (NULL, NULL, width, height);
cairo_t *cr = cairo_create(surface);
rsvg_handle_render_cairo(handle, cr);
rsvg_handle_close(handle, NULL);
g_object_unref(handle);
cairo_pattern_t *pattern = cairo_pattern_create_for_surface (surface);
certainly seems to give a blurry result when I use pattern as a mask for
rendering to the final surface.
If this is not another example of the same thing, please let me know!
This is similar to the fallback resolution bug where images acquired from the recording surface it at a fixed resolution. With the fallback resolution bug now fixed it should not be hard to fix this. I have an experimental patch here http://cgit.freedesktop.org/~ajohnson/cairo/commit/?h=fix-blurry-copy-from-pdf-surface&id=6de38c2a32095296fa23c21dd8720936e57aebb1 that makes your test case work. However it causes a few test failures in the test suite that will need investigating. The sample program in comment 1 works with cairo 1.11.4 if you change the pdf surface to a recording surface. I'm not sure why it is still not working for paginated surfaces. I believe Adrian tricked me into fixing this for releasing 1.12. ;-) Please do test. |
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