Sets the current font matrix to a scale by a factor of size, replacing any font matrix previously set with cairo_set_font_size() or cairo_set_font_matrix(). This results in a font size of size user space units. (More precisely, this matrix will result in the font's em-square being a size by size square in user space.) If text is drawn without a call to cairo_set_font_size(), (nor cairo_set_font_matrix() nor cairo_set_scaled_font()), the default font size is 10.0. Since 1.0

class Context
double size


size double

the new font size, in user space units