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diff --git a/src/display/nr-filter-primitive.h b/src/display/nr-filter-primitive.h
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+++ b/src/display/nr-filter-primitive.h
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+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * SVG filters rendering
+ *
+ * Author:
+ *   Niko Kiirala <niko@kiirala.com>
+ *
+ * Copyright (C) 2006-2007 Niko Kiirala
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+#ifndef SEEN_NR_FILTER_PRIMITIVE_H
+#define SEEN_NR_FILTER_PRIMITIVE_H
+
+#include <2geom/forward.h>
+#include <2geom/rect.h>
+
+#include <glibmm/ustring.h>
+
+#include "display/nr-filter-types.h"
+#include "svg/svg-length.h"
+
+class SPStyle;
+
+namespace Inkscape {
+namespace Filters {
+
+class FilterSlot;
+class FilterUnits;
+
+class FilterPrimitive {
+public:
+    FilterPrimitive();
+    virtual ~FilterPrimitive();
+
+    virtual void render_cairo(FilterSlot &slot);
+    virtual int render(FilterSlot & /*slot*/, FilterUnits const & /*units*/) { return 0; } // pure virtual?
+    virtual void area_enlarge(Geom::IntRect &area, Geom::Affine const &m);
+
+    /**
+     * Sets the input slot number 'slot' to be used as input in rendering
+     * filter primitive 'primitive'
+     * For filter primitive types accepting more than one input, this sets the
+     * first input.
+     * If any of the required input slots is not set, the output of previous
+     * filter primitive is used, or SourceGraphic if this is the first
+     * primitive for this filter.
+     */
+    virtual void set_input(int slot);
+
+    /**
+     * Sets the input slot number 'slot' to be user as input number 'input' in
+     * rendering filter primitive 'primitive'
+     * First input for a filter primitive is number 0. For primitives with
+     * attributes 'in' and 'in2', these are numbered 0 and 1, respectively.
+     * If any of required input slots for a filter is not set, the output of
+     * previous filter primitive is used, or SourceGraphic if this is the first
+     * filter primitive for this filter.
+     */
+    virtual void set_input(int input, int slot);
+
+    /**
+     * Sets the slot number 'slot' to be used as output from filter primitive
+     * 'primitive'
+     * If output slot for a filter element is not set, one of the unused image
+     * slots is used.
+     * It is an error to specify a pre-defined slot as 'slot'. Such call does
+     * not have any effect to the state of filter or its primitives.
+     */
+    virtual void set_output(int slot);
+
+    // returns cache score factor, reflecting the cost of rendering this filter
+    // this should return how many times slower this primitive is that normal rendering
+    virtual double complexity(Geom::Affine const &/*ctm*/) { return 1.0; }
+
+    virtual bool uses_background() {
+        if (_input == NR_FILTER_BACKGROUNDIMAGE || _input == NR_FILTER_BACKGROUNDALPHA) {
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    /**
+     * Sets the filter primitive subregion. Passing an unset length
+     * (length._set == false) WILL change the parameter as it is
+     * important to know if a parameter is unset.
+     */
+    void set_x(SVGLength const &length);
+    void set_y(SVGLength const &length);
+    void set_width(SVGLength const &length);
+    void set_height(SVGLength const &length);
+    void set_subregion(SVGLength const &x, SVGLength const &y,
+                       SVGLength const &width, SVGLength const &height);
+
+    /**
+     * Resets the filter primitive subregion to its default value
+     */
+    void reset_subregion(); // Not implemented
+
+    /**
+     * Returns the filter primitive area in user coordinate system.
+     */
+    Geom::Rect filter_primitive_area(FilterUnits const &units);
+
+    /**
+     *Indicate whether the filter primitive can handle the given affine.
+     *
+     * Results of some filter primitives depend on the coordinate system used when rendering.
+     * A gaussian blur with equal x and y deviation will remain unchanged by rotations.
+     * Per-pixel filters like color matrix and blend will not change regardless of
+     * the transformation.
+     *
+     * When any filter returns false, filter rendering is performed on an intermediate surface
+     * with edges parallel to the axes of the user coordinate system. This means
+     * the matrices from FilterUnits will contain at most a (possibly non-uniform) scale
+     * and a translation. When all primitives of the filter return true, the rendering is
+     * performed in display coordinate space and no intermediate surface is used.
+     */
+    virtual bool can_handle_affine(Geom::Affine const &) { return false; }
+
+    /**
+     * Sets style for access to properties used by filter primitives.
+     */
+    void setStyle(SPStyle *style);
+
+    // Useful for debugging
+    virtual Glib::ustring name() { return Glib::ustring("No name"); }
+
+protected:
+    int _input;
+    int _output;
+
+    /* Filter primitive subregion */
+    SVGLength _subregion_x;
+    SVGLength _subregion_y;
+    SVGLength _subregion_width;
+    SVGLength _subregion_height;
+
+    SPStyle *_style;
+};
+
+
+} /* namespace Filters */
+} /* namespace Inkscape */
+
+#endif /* SEEN_NR_FILTER_PRIMITIVE_H */
+/*
+  Local Variables:
+  mode:c++
+  c-file-style:"stroustrup"
+  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
+  indent-tabs-mode:nil
+  fill-column:99
+  End:
+*/
+// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:fileencoding=utf-8:textwidth=99 :