Commit cfc67afe authored by Adrian Johnson's avatar Adrian Johnson Committed by Carlos Garcia Campos

cairo: fix stroking of very thin lines

Lines with a width less than 1.0 are almost invisible in cairo output
due to antialising. The PDF standard states that when the Stroke
Adjust graphics parameter is true, all lines must be at least one pixel wide.

Add a stroke_adjust flag to the CairoOuputDev. Like splash, use the
globalParam strokeAdjust setting (which defaults to true) to
initialize the flag and ignore the Stroke Adjust settng in PDF
files. This emulates Acrobat behavior.

When stroke_adjust is true, find the line width in device pixels and
if less than 0.5 set the line width to 0.5 device pixels. The value
0.5 pixels seems to make horizontal and vertical lines look better
because integer aligned 1.0 wide lines in cairo are rendered two
pixels wide which looks too fat.
parent 7a7c932e
......@@ -153,6 +153,10 @@ CairoOutputDev::CairoOutputDev() {
text = NULL;
actualText = NULL;
// the SA parameter supposedly defaults to false, but Acrobat
// apparently hardwires it to true
stroke_adjust = globalParams->getStrokeAdjust();
CairoOutputDev::~CairoOutputDev() {
......@@ -420,7 +424,21 @@ void CairoOutputDev::updateLineWidth(GfxState *state) {
cairo_device_to_user_distance(cairo, &x, &y);
cairo_set_line_width (cairo, MIN(fabs(x),fabs(y)));
} else {
cairo_set_line_width (cairo, state->getLineWidth());
double width = state->getLineWidth();
if (stroke_adjust && !printing) {
double x, y;
x = y = width;
/* find out line width in device units */
cairo_user_to_device_distance(cairo, &x, &y);
if (x < 0.5 && y < 0.5) {
/* adjust width to at least one device pixel */
x = y = 0.5;
cairo_device_to_user_distance(cairo, &x, &y);
width = MIN(fabs(x),fabs(y));
cairo_set_line_width (cairo, width);
if (cairo_shape)
cairo_set_line_width (cairo_shape, cairo_get_line_width (cairo));
......@@ -287,6 +287,7 @@ protected:
cairo_pattern_t *fill_pattern, *stroke_pattern;
double fill_opacity;
double stroke_opacity;
GBool stroke_adjust;
CairoFont *currentFont;
struct StrokePathClip {
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