1 files changed, 92 insertions, 0 deletions
diff --git a/src/util/preview.cpp b/src/util/preview.cpp
new file mode 100644
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--- /dev/null
+++ b/src/util/preview.cpp
@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/**
+ * @file
+ * Utility functions for generating export previews.
+ */
+/* Authors:
+ *   Anshudhar Kumar Singh <anshudhar2001@gmail.com>
+ *   Martin Owens <doctormo@gmail.com>
+ *
+ * Copyright (C) 2021 Anshudhar Kumar Singh
+ *               2021 Martin Owens
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#include "preview.h"
+
+#include "document.h"
+#include "display/cairo-utils.h"
+#include "display/drawing-context.h"
+#include "object/sp-namedview.h"
+#include "object/sp-root.h"
+#include "async/async.h"
+
+namespace Inkscape {
+namespace UI {
+namespace Preview {
+
+Cairo::RefPtr<Cairo::ImageSurface>
+render_preview(SPDocument *doc, std::shared_ptr<Inkscape::Drawing> drawing, uint32_t bg,
+               Inkscape::DrawingItem *item, unsigned width_in, unsigned height_in, Geom::Rect const &dboxIn)
+{
+    if (!drawing->root())
+        return {};
+
+    // Calculate a scaling factor for the requested bounding box.
+    double sf = 1.0;
+    Geom::IntRect ibox = dboxIn.roundOutwards();
+    if (ibox.width() != width_in || ibox.height() != height_in) {
+        sf = std::min((double)width_in / dboxIn.width(),
+                      (double)height_in / dboxIn.height());
+        auto scaled_box = dboxIn * Geom::Scale(sf);
+        ibox = scaled_box.roundOutwards();
+    }
+
+    auto pdim = Geom::IntPoint(width_in, height_in);
+    // The unsigned width/height can wrap around when negative.
+    int dx = ((int)width_in - ibox.width()) / 2;
+    int dy = ((int)height_in - ibox.height()) / 2;
+    auto area = Geom::IntRect::from_xywh(ibox.min() - Geom::IntPoint(dx, dy), pdim);
+
+    /* Actual renderable area */
+    Geom::IntRect ua = *Geom::intersect(ibox, area);
+    auto surface = Cairo::ImageSurface::create(Cairo::FORMAT_ARGB32, ua.width(), ua.height());
+
+    {
+        auto cr = Cairo::Context::create(surface);
+        cr->rectangle(0, 0, ua.width(), ua.height());
+
+        // We always use checkerboard to indicate transparency.
+        if (SP_RGBA32_A_F(bg) < 1.0) {
+            auto pattern = ink_cairo_pattern_create_checkerboard(bg, false);
+            auto background = Cairo::RefPtr<Cairo::Pattern>(new Cairo::Pattern(pattern, true));
+            cr->set_source(background);
+            cr->fill();
+        }
+
+        // We always draw the background on top to indicate partial backgrounds.
+        cr->set_source_rgba(SP_RGBA32_R_F(bg), SP_RGBA32_G_F(bg), SP_RGBA32_B_F(bg), SP_RGBA32_A_F(bg));
+        cr->fill();
+    }
+
+    // Resize the contents to the available space with a scale factor.
+    drawing->root()->setTransform(Geom::Scale(sf));
+    drawing->update();
+
+    auto dc = Inkscape::DrawingContext(surface->cobj(), ua.min());
+    if (item) {
+        // Render just one item
+        item->render(dc, ua);
+    } else {
+        // Render drawing.
+        drawing->render(dc, ua);
+    }
+
+    surface->flush();
+    return surface;
+}
+
+} // namespace Preview
+} // namespace UI
+} // namespace Inkscape