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22.6 Groups and Transparency

Some document formats (such as PDF) offer a rich transparency model that allows graphical objects to be ’Grouped’ together and imposed upon the page as if they have a given opacity, using a variety of different blend modes.

MuPDF implements this by using the fz_begin_group and fz_end_group calls.

void fz_begin_group(fz_context *ctx, fz_device *dev, const fz_rect *area, int isolated, int knockout, int blendmode, float alpha); 
void fz_end_group(fz_context *ctx, fz_device *dev);

The exact details of PDF transparency are too complex to explain here; for a full explanation see The PDF Reference Manual.

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