所以我正在尝试在Cairo中设置遮罩,但是无法使其产生任何影响。下面我有一个简单的程序,基于这个程序:http://snipplr.com/view/22584/cairo-hello-world-examble/。
我设置了一个完全透明的遮罩,所以不应该画出任何东西,但似乎没有任何效果-文本仍然被绘制。我的代码如下。我错过了什么?
谢谢!
int main(int argc, char* argv[])
{
cairo_surface_t* surface;
cairo_t* cr;
surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, 200, 40);
cr = cairo_create (surface);
//****
// Here I create a pattern with an alpha of zero and set it to be cairo's mask
// According to http://www.cairographics.org/manual/cairo-context.html#cairo-mask
// "Opaque areas of pattern are painted with the source, transparent areas are not painted."
// Shouldn't this make it so nothing gets drawn?
//****
cairo_pattern_t* nothing = cairo_pattern_create_rgba(0,0,0,0);
cairo_mask (cr, nothing);
cairo_text_extents_t te;
cairo_set_source_rgb (cr, 0.0, 0.0, 0.0);
cairo_select_font_face (cr, "Georgia",
CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);
cairo_set_font_size (cr, 20.0);
cairo_text_extents (cr, "hello cairo!", &te);
cairo_move_to (cr, 20, 20);
cairo_show_text (cr, "hello cairo!");
cairo_fill(cr);
// An image gets drawn that says "hello cairo!" in big letters
cairo_surface_write_to_png(surface, "hello_cairo.png");
return 0;
}