Question

我希望能够从开罗表面制作GtkImage（无需编写临时文件）。

我目前将表面作为PNG写入一个char数组，然后我将其提供给PixbufLoader以获取我用来创建GtkImage的Pixbuf：

typedef struct
{
    unsigned char *pos;
    unsigned char *end;
} closure_t;

static cairo_status_t
png_to_array (void *closure, const unsigned char *data, unsigned int length)
{
    closure_t *cl = (closure_t *) closure;

    if ((cl->pos + length) > (cl->end))
        return CAIRO_STATUS_WRITE_ERROR;

    memcpy (cl->pos, data, length);
    cl->pos += length;

    return CAIRO_STATUS_SUCCESS;
}


// later in the code
cairo_surface_t *surface = ...

...

// how would i determine the right size?
unsigned char arr[...];
closure_t cl;
GtkWidget *image;
GdkPixbufLoader *pbloader;
GdkPixbuf *pb;

// copy surface png to arr
cl.pos = arr;
cl.end = arr + sizeof(arr);
cairo_surface_write_to_png_stream (surface,
                    (cairo_write_func_t) png_to_array,
                    &cl);

...
// write to pixbufloader, get pixbuf, create image
pbloader = gdk_pixbuf_loader_new();
gdk_pixbuf_loader_write(pbloader, arr, sizeof(arr), NULL);
gdk_pixbuf_loader_close(pbloader, NULL);

pb = gdk_pixbuf_loader_get_pixbuf(pbloader);

image = gtk_image_new_from_pixbuf(pb);

这看起来相当麻烦 - 是不是有更简单的方法来做到这一点？
如何在我的示例中确定数组的大小？

Answer 1

一个功能可以为您节省大量精力。查找gdk_pixbuf_get_from_surface。它从cairo_surface_t获取一个Pixbuf。粗略的，在他写的时候意识到，只有你使用Gdk-3.0，这也意味着使用Gtk + -3.0。

粗略如果你想使用Gtk + -2.0那么你可以创建一个像素图，从中获取一个cairo_t然后通过

将你的另一个cairo_surface_t复制到它

cairo_set_source_surface (cr, surface, x0, y0);
cairo_rectangle (cr, x0 + x, y0 + y, width, height);
cairo_fill (cr);

下面是一个如何创建像素图的示例，我将让您填写其余部分。

#include <gtk/gtk.h>
#include <cairo/cairo.h>


int main(gint argc, gchar *argv[])
{
    GdkPixmap *pixmap;
    GtkWidget *image;
    GtkWidget *window;
    cairo_t *cr;

    gtk_init(&argc, &argv);

    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    g_signal_connect(G_OBJECT(window), "delete-event", G_CALLBACK(gtk_main_quit), NULL);

    gtk_widget_show_all(window);

    pixmap = gdk_pixmap_new(window->window, 100, 100, -1);
    cr = gdk_cairo_create(pixmap);
    cairo_set_source_rgb(cr, 0.0, 0.0, 0.0);    
    cairo_rectangle(cr, 10, 10, 80, 80);
    cairo_fill(cr);
    cairo_destroy(cr);

    cr = NULL;



    image = gtk_image_new_from_pixmap(pixmap, NULL);

    gtk_container_add(GTK_CONTAINER(window), image);


    gtk_widget_show(image);



    gtk_main();

    return 0;
}

Answer 2

只是一个提示，我不确定如何确定数组的大小，但是我确定数组的大小应该多长时间，因为您的png_to_array回调将被调用为数组大小的几倍。是所有长度的总和

我正在使用跨步来确定数组的大小，但最后，total_lenght将确定png的大小

int total_lenght = 0;

typedef struct
{
    unsigned char *pos;
    unsigned char *end;
} closure_t;

static cairo_status_t
png_to_array (void *closure, const unsigned char *data, unsigned int length)
{
    closure_t *cl = (closure_t *) closure;

    if ((cl->pos + length) > (cl->end))
        return CAIRO_STATUS_WRITE_ERROR;

    memcpy (cl->pos, data, length);
    cl->pos += length;

    total_lenght += lenght;

    return CAIRO_STATUS_SUCCESS;
}


// later in the code
cairo_surface_t *surface = ...

...

int stride = cairo_image_surface_get_stride(surface);

unsigned char *arr = (unsigned char *) malloc(stride);
closure_t cl;
GtkWidget *image;
GdkPixbufLoader *pbloader;
GdkPixbuf *pb;

// copy surface png to arr
cl.pos = arr;
cl.end = arr + stride;
cairo_surface_write_to_png_stream (surface,
                    (cairo_write_func_t) png_to_array,
                    &cl);

...
// write to pixbufloader, get pixbuf, create image
pbloader = gdk_pixbuf_loader_new();
gdk_pixbuf_loader_write(pbloader, arr, total_lenght), NULL);
gdk_pixbuf_loader_close(pbloader, NULL);

pb = gdk_pixbuf_loader_get_pixbuf(pbloader);

image = gtk_image_new_from_pixbuf(pb);

如何从开罗表面创建GtkImage？

2 个答案: