问题描述
我已经为C渲染了一个示例。我的意思是，使用Cairo的最小C程序显示了Here。 但是，当我尝试渲染此代码时：
<p>ampm true: <span id="time1"></span> (default)</p>
<p>ampm false: <span id="time2"></span></p>我得到一个空的png。看起来好像有东西，但没有画出来。 我编译：
#include <cairo.h>
int main(void){
/* Where we gonna draw. The image to print. */
cairo_surface_t *surface;
/* The context. The printed layer by a surface */
cairo_t *cr;
/* The format (in this case ARGB),width and height of surface */
surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32,120,120);
/* The context behind of surface */
cr = cairo_create(surface);
/* void cairo_set_source_rgb(cairo_t *cr,double red,double green,double blue); */
cairo_set_source_rgb(cr,0);
/* void cairo_move_to(cairo_t *cr,double x,double y); */
/* After this call the current point will be (x,y). */
cairo_move_to (cr,0);
/* void cairo_line_to(cairo_t *cr,double y); */
/* Adds a line to the path from the current position (x,y). After this call the current point will be (x,y). */
/* Must be a current point,otherwise the beahavior gonna be like move_to */
cairo_line_to (cr,1,1);
cairo_move_to (cr,0);
cairo_line_to (cr,1);
/* void cairo_set_line_width(cairo_t *cr,double width); */
/* Sets the current line width within the cairo context. The line width value specifies the diameter of a pen is circular */
cairo_set_line_width (cr,0.2);
/* void cairo_stroke(cairo_t *cr); */
/* A drawing operator that strokes the current path according to the current line width,line join,line cap,and dash settings. */
cairo_stroke (cr);
/* void cairo_rectangle(cairo_t *cr,double y,double width,double height); */
/* Adds a closed sub-path rectangle of the given size to the current path at position (x,y) in user-space coordinates. */
/* This function is logically equivalent to:
* cairo_move_to (cr,x,y);
* cairo_rel_line_to (cr,width,0);
* cairo_rel_line_to (cr,height);
* cairo_rel_line_to (cr,-width,0);
* cairo_close_path (cr);
* *************************************/
cairo_rectangle (cr,0.5,0.5);
/* cairo_set_source_rgba(cairo_t *cr,double blue,double alpha); */
/* Sets the source pattern within cr to a translucent color. This color will then be used for any subsequent drawing operation
* until a new source pattern is set.
* The color and alpha components are floating point numbers in the range 0 to 1. If the values passed in are outside that range,* they will be clamped.
* The default source pattern is opaque black,(that is,it is equivalent to cairo_set_source_rgba(cr,0.0,1.0)).
* *****************************************************************************************************************************/
cairo_set_source_rgba (cr,0.80);
/* void cairo_fill(cairo_t *cr); */
/* A drawing operator that fills the current path according to the current fill rule,(each sub-path is implicitly closed before
* being filled). After cairo_fill(),the current path will be cleared from the cairo context.
* *****************************************************************************************************************************/
cairo_fill (cr);
cairo_rectangle (cr,0.5);
cairo_set_source_rgba (cr,0.60);
cairo_fill (cr);
cairo_rectangle (cr,0.40);
cairo_fill (cr);
cairo_surface_write_to_png(surface,"image.png");
cairo_destroy(cr);
cairo_surface_destroy(surface);
return 0;
}
我的cc -o file $(pkg-config --cflags --libs cairo) file.c超出了这个范围：
brew info Cairo cairo: stable 1.16.0 (bottled),HEAD
Vector graphics library with cross-device output support
https://cairographics.org/
/usr/local/Cellar/cairo/1.16.0_3 (117 files,5.7MB) *
Poured from bottle on 2020-10-12 at 00:17:34
From: https://github.com/Homebrew/homebrew-core/blob/HEAD/Formula/cairo.rb
License: LGPL-2.1
==> Dependencies
Build: pkg-config ✔
required: fontconfig ✔,freetype ✔,glib ✔,libpng ✔,lzo ✔,pixman ✔
==> Options
--HEAD
Install HEAD version
==> Analytics
install: 110,282 (30 days),348,240 (90 days),254,903 (365 days)
install-on-request: 13,651 (30 days),54,037 (90 days),132,345 (365 days)
build-error: 0 (30 days)
和pkg-config Cflags：
-L/usr/local/Cellar/cairo/1.16.0_3/lib -lcairo有什么看不见的错误吗？一切看起来很棒。我不知道会发生什么。
解决方法
cairo_rectangle (cr,0.5,0.5);
您似乎假设坐标在0..1范围内，可以覆盖整个表面。
这不是事实。取而代之的是，坐标织布来自0..width和0..height。
您的指令将创建一个在每个方向上都有半个像素的矩形，并且线宽之前设置为1/5像素。这些坐标不会让您看到太多。
您链接的样本使用大得多的值。试试看。