[cairo] Recording surfaces fail to replay onto SVG surfaces

[Antony Lee]

Hi all,

I am having an issue with replaying a recording surface onto an SVG
surface.  A minimal example is included at the end of the email.

Briefly, the example sets up a recording surface and two 100x100 surfaces
-- one IMAGE and one SVG.  It then draws a 10x10 rectangle on each of them
at position (10, 10) and saves the results (the IMAGE to a PNG).  Both
resulting files display the box at the correct position.

The example then tries to replay the recording surface onto a separate
100x100 SVG surface, and also save that surface.  Unfortunately, this
results in a blank SVG.  Note that if, instead, the recording surface is
played onto a separate 100x100 IMAGE surface (code not included for
simplicity), this works perfectly well (the resulting PNG also displays the
box); so the basic setup of the recording surface seems correct.

I am using cairo 1.15.8 from Arch Linux.

Any help would be very welcome.  Thanks!

Antony Lee



=== Example program; compile and run with:
    gcc main.c $(pkg-config --cflags --libs cairo) -o main && ./main

#include <stddef.h>
#include <cairo/cairo.h>
#include <cairo/cairo-svg.h>

int main() {
  cairo_surface_t* rec_surf =
cairo_recording_surface_create(CAIRO_CONTENT_COLOR_ALPHA, NULL);
  cairo_t* rec_ctx = cairo_create(rec_surf);

  cairo_surface_t* img_surf =
cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 100, 100);
  cairo_t* img_ctx = cairo_create(img_surf);

  cairo_surface_t* svg_surf = cairo_svg_surface_create("/tmp/test.svg",
100, 100);
  cairo_t* svg_ctx = cairo_create(svg_surf);

  cairo_t* ctxs[3] = {rec_ctx, img_ctx, svg_ctx};

  for (unsigned i = 0; i < 3; ++i) {
    cairo_rectangle(ctxs[i], 10, 10, 10, 10);
    cairo_fill(ctxs[i]);
  }

  // Dump image to png.
  cairo_surface_write_to_png(img_surf, "/tmp/test.png");

  // Transfer recording surface to SVG.
  cairo_surface_t* svg1_surf = cairo_svg_surface_create("/tmp/test1.svg",
100, 100);
  cairo_t* svg1_ctx = cairo_create(svg1_surf);
  cairo_set_source_surface(svg1_ctx, rec_surf, 0, 0);
  cairo_paint(svg1_ctx);

  // Done.
  for (unsigned i = 0; i < 3; ++i) {
    if (cairo_status(ctxs[i])) {
      return 1;
    }
  }
  cairo_surface_finish(svg_surf);
  cairo_surface_finish(svg1_surf);
  for (unsigned i = 0; i < 3; ++i) {
    cairo_surface_destroy(cairo_get_target(ctxs[i]));
    cairo_destroy(ctxs[i]);
  }
  cairo_surface_destroy(svg1_surf);
  cairo_destroy(svg1_ctx);
}
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