<div dir="ltr">[I previously posted this on stackoverflow, but that appears not to be the best forum for the question.]While using Cairo 1.14.6 for display purposes, I found that overwriting the very same path with another color does not necessarily overwrite all pixels, and leaves undesirable artifacts behind.As evidence of my claim I offer this output from a short self-contained example, the source for which follows further below.<a href="http://i.stack.imgur.com/QBXjh.png" rel="nofollow" style="margin:0px;padding:0px;border:0px;color:rgb(0,89,153);text-decoration:none"><img src="http://i.stack.imgur.com/QBXjh.png" alt="enter image description here" style="margin: 0px; padding: 0px; border: 0px; max-width: 100%;"></a>An explanation of the six parts of the image, from left to right:<ol style="margin:0px 0px 1em 30px;padding:0px;border:0px;font-size:15px;color:rgb(36,39,41);font-family:arial,"helvetica neue",helvetica,sans-serif;line-height:19.5px"><li style="margin:0px 0px 0.5em;padding:0px;border:0px;word-wrap:break-word">Original shape stroked in blue.</li><li style="margin:0px 0px 0.5em;padding:0px;border:0px;word-wrap:break-word">Original shape overwritten in RGBA white.</li><li style="margin:0px 0px 0.5em;padding:0px;border:0px;word-wrap:break-word">Original shape overwritten in RGB white.</li><li style="margin:0px 0px 0.5em;padding:0px;border:0px;word-wrap:break-word">Original shape overwritten in RGBA white with CAIRO_OPERATOR_SOURCE mode.</li><li style="margin:0px 0px 0.5em;padding:0px;border:0px;word-wrap:break-word">Original shape overwritten in RGBA white with CAIRO_OPERATOR_SOURCE mode and CAIRO_ANTIALIAS_NONE.</li><li style="margin:0px;padding:0px;border:0px;word-wrap:break-word">Original shape overwritten in RGBA white with CAIRO_OPERATOR_SOURCE mode and CAIRO_ANTIALIAS_BEST.</li></ol>The image was generated from the following code:<pre class="gmail-lang-c gmail-prettyprint gmail-prettyprinted" style="margin-top:0px;margin-bottom:1em;padding:5px;border:0px;font-size:13px;width:auto;max-height:600px;overflow:auto;font-family:consolas,menlo,monaco,"lucida console","liberation mono","dejavu sans mono","bitstream vera sans mono","courier new",monospace,sans-serif;color:rgb(57,51,24);word-wrap:normal;background-color:rgb(239,240,241)"><code style="margin:0px;padding:0px;border:0px;font-family:consolas,menlo,monaco,"lucida console","liberation mono","dejavu sans mono","bitstream vera sans mono","courier new",monospace,sans-serif;white-space:inherit">#include "cairo/cairo.h" #define M_PI 3.14159265358979323846 void draw_shape(cairo_t* cr, int x, int y) { cairo_arc(cr, 50 + x, 50 + y, 48, -M_PI, -M_PI / 2); cairo_stroke(cr); cairo_move_to(cr, x + 2, y + 2); cairo_line_to(cr, x + 48, y + 48); cairo_stroke(cr); } int main(int argc, char** argv) { int x = 0; int y = 0; cairo_surface_t* surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 300, 50); cairo_t* cr = cairo_create(surface); /* Draw a white background and a few shapes to overwrite */ cairo_set_source_rgba(cr, 1.0, 1.0, 1.0, 1.0); cairo_paint(cr); cairo_set_source_rgba(cr, 0.0, 0.0, 1.0, 1.0); draw_shape(cr, x, y); x += 50; draw_shape(cr, x, y); x += 50; draw_shape(cr, x, y); x += 50; draw_shape(cr, x, y); x += 50; draw_shape(cr, x, y); x += 50; draw_shape(cr, x, y); x += 50; x = 50; /* Leftmost shape is left unchanged for reference */ /* Stroke in RGBA opaque white */ cairo_set_source_rgba(cr, 1.0, 1.0, 1.0, 1.0); draw_shape(cr, x, y); x += 50; /* Stroke in RGB white */ cairo_set_source_rgb(cr, 1.0, 1.0, 1.0); draw_shape(cr, x + 0, y); x += 50; /* Stroke in opaque white without blending */ cairo_set_source_rgba(cr, 1.0, 1.0, 1.0, 1.0); cairo_set_operator(cr, CAIRO_OPERATOR_SOURCE); draw_shape(cr, x, y); x += 50; /* Stroke in opaque white without blending, with no antialiasing */ cairo_set_source_rgba(cr, 1.0, 1.0, 1.0, 1.0); cairo_set_operator(cr, CAIRO_OPERATOR_SOURCE); cairo_set_antialias(cr, CAIRO_ANTIALIAS_NONE); draw_shape(cr, x, y); x += 50; /* Stroke in opaque white without blending, with best antialiasing */ cairo_set_source_rgba(cr, 1.0, 1.0, 1.0, 1.0); cairo_set_operator(cr, CAIRO_OPERATOR_SOURCE); cairo_set_antialias(cr, CAIRO_ANTIALIAS_BEST); draw_shape(cr, x, y); x += 50; /* Write the results to a file */ cairo_surface_write_to_png(surface, "output.png"); return 0; }</code></pre>It doesn't make intuitive sense to me that overwriting the very same shape would not overwrite all of its pixels, especially if I force it into non-blending CAIRO_OPERATOR_SOURCE mode. The results are the same on the framebuffer that constitutes my actual surface, so this is not an issue with the backend.Cairo is usually so good at what it does that I'm very surprised at this. Is there no way to overwrite an anti-aliased shape exactly in Cairo?Josh</div>