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45 lines
1.8 KiB
Markdown
45 lines
1.8 KiB
Markdown
Title: Scaling and compositing
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----
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The `GdkPixBuf` class contains methods to scale pixbufs, to scale
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pixbufs and alpha blend against an existing image, and to scale
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pixbufs and alpha blend against a solid color or checkerboard.
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Alpha blending a checkerboard is a common way to show an image with
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an alpha channel in image-viewing and editing software.
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Note that in these functions, the terms ‘alpha blending’ and ‘compositing’
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are used synonymously.
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Since the full-featured functions [method@GdkPixbuf.Pixbuf.scale],
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[method@GdkPixbuf.Pixbuf.composite], and [`method@GdkPixbuf.Pixbuf.composite_color`]
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are rather complex to use and have many arguments, two simple
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convenience functions are provided, [`method@GdkPixbuf.Pixbuf.scale_simple`]
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and [`method@GdkPixbuf.Pixbuf.composite_color_simple`] which create a new
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pixbuf of a given size, scale an original image to fit, and then return it.
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If the destination pixbuf was created from a read only source, these
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operations will force a copy into a mutable buffer.
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Scaling and alpha blending functions take advantage of MMX hardware
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acceleration on systems where MMX is supported. If `GdkPixbuf` is built
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with the Sun mediaLib library, these functions are instead accelerated
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using mediaLib, which provides hardware acceleration on Intel, AMD,
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and Sparc chipsets. If desired, mediaLib support can be turned off by
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setting the `GDK_DISABLE_MEDIALIB` environment variable.
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The alpha blending function used is:
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```
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Cd = Cs·As + Cd(1-As)
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```
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where `Cd` is the destination pixel color, `Cs` is the source pixel color,
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and `As` is the source pixel alpha.
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**NOTE**: It is recommended to use [Cairo][cairo] for scaling and
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compositing, by using the contents of a `GdkPixbuf` pixel buffer as the
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data for a Cairo image surface.
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[cairo]: https://www.cairographics.org
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