cairo自定义surface

Cairo是一个功能强大的2D图形库，它支持多种绘图表面(surface)。其中，通过自定义surface，我们可以实现自己的绘图目的。

在Cairo中，Surface是一个表示要绘制的目标的抽象概念。Surface可以是一个窗口、一个图片文件、一个PDF文件等等。要创建一个自定义的surface对象，你需要定义一个Cairo_surface_t结构体，该结构体包含了一些函数指针，用于绑定你的自定义surface对象与Cairo库中的相关函数。

下面是一些示例代码，用于创建一个自定义的surface对象：

#include <cairo.h>

typedef struct _MySurface {
    cairo_surface_t base;
    // Define your own properties here
} MySurface;

static cairo_status_t my_surface_finish(cairo_surface_t *surface) {
    // Define your own cleanup code here
    return CAIRO_STATUS_SUCCESS;
}

static cairo_status_t my_surface_flush(cairo_surface_t *surface) {
    // Define your own flush code here
    return CAIRO_STATUS_SUCCESS;
}

static cairo_status_t my_surface_write_to_png(cairo_surface_t *surface, const char *filename) {
    // Define your own code to write to PNG file here
    return CAIRO_STATUS_SUCCESS;
}

static cairo_surface_t *my_surface_create_similar(cairo_surface_t *surface, cairo_content_t content, int width, int height) {
    // Define your own code to create a similar surface here
    return NULL;
}

static cairo_surface_t *my_surface_create_similar_image(cairo_surface_t *surface, cairo_format_t format, int width, int height) {
    // Define your own code to create a similar image surface here
    return NULL;
}

static cairo_surface_t *my_surface_create_for_rectangle(cairo_surface_t *surface, double x, double y, double width, double height) {
    // Define your own code to create a surface for a rectangle here
    return NULL;
}

static cairo_surface_t *my_surface_create_observer(cairo_surface_t *surface, cairo_surface_observer_mode_t mode) {
    // Define your own code to create an observer surface here
    return NULL;
}

static cairo_int_status_t my_surface_acquire_source_image(cairo_surface_t *surface, cairo_image_surface_t **image_out, void **extra_data_out) {
    // Define your own code to acquire a source image here
    return CAIRO_INT_STATUS_UNSUPPORTED;
}

static void my_surface_release_source_image(cairo_surface_t *surface, cairo_image_surface_t *image, void *extra_data) {
    // Define your own code to release the source image here
}

static cairo_int_status_t my_surface_acquire_dest_image(cairo_surface_t *surface, cairo_rectangle_t *interest_rect, cairo_image_surface_t **image_out, cairo_rectangle_t *image_rect_out, void **extra_data_out) {
    // Define your own code to acquire a destination image here
    return CAIRO_INT_STATUS_UNSUPPORTED;
}

static void my_surface_release_dest_image(cairo_surface_t *surface, cairo_rectangle_t *interest_rect, cairo_image_surface_t *image, cairo_rectangle_t *image_rect, void *extra_data) {
    // Define your own code to release the destination image here
}

static cairo_bool_t my_surface_get_extents(cairo_surface_t *surface, cairo_rectangle_t *rectangle) {
    // Define your own code to get the extents of the surface here
    return FALSE;
}

static cairo_surface_t *my_surface_map_to_image(cairo_surface_t *surface, cairo_rectangle_t *extents) {
    // Define your own code to map the surface to an image here
    return NULL;
}

static void my_surface_unmap_image(cairo_surface_t *surface, cairo_surface_t *image) {
    // Define your own code to unmap the image here
}

static cairo_surface_t *my_surface_map_to_image_surface(cairo_surface_t *surface, cairo_rectangle_t *extents, cairo_format_t format, void **data_out, int *stride_out) {
    // Define your own code to map the surface to an image surface here
    return NULL;
}

static void my_surface_unmap_image_surface(cairo_surface_t *surface, cairo_surface_t *image_surface, void *data) {
    // Define your own code to unmap the image surface here
}

static cairo_status_t my_surface_snapshot(cairo_surface_t *surface, cairo_surface_t **snapshot_out) {
    // Define your own code to snapshot the surface here
    return CAIRO_STATUS_SUCCESS;
}

static cairo_surface_t *my_surface_copy_page(cairo_surface_t *surface) {
    // Define your own code to copy a page of the surface here
    return NULL;
}

static cairo_status_t my_surface_show_page(cairo_surface_t *surface) {
    // Define your own code to show a page of the surface here
    return CAIRO_STATUS_SUCCESS;
}

static cairo_bool_t my_surface_has_show_text_glyphs(cairo_surface_t *surface) {
    // Define your own code to determine if the surface supports show_text_glyphs here
    return FALSE;
}

static cairo_status_t my_surface_show_text_glyphs(cairo_surface_t *surface, const char *utf8, int utf8_len, const cairo_glyph_t *glyphs, int num_glyphs, const cairo_text_cluster_t *clusters, int num_clusters, const cairo_text_cluster_flags_t *cluster_flags) {
    // Define your own code to support show_text_glyphs here
    return CAIRO_STATUS_SUCCESS;
}

static cairo_bool_t my_surface_supports_mime_type(cairo_surface_t *surface, const char *mime_type) {
    // Define your own code to determine if the surface supports a MIME type here
    return FALSE;
}

static cairo_status_t my_surface_set_mime_data(cairo_surface_t *surface, const char *mime_type, const unsigned char *data, unsigned long length, cairo_destroy_func_t destroy, void *closure) {
    // Define your own code to set MIME data here
    return CAIRO_STATUS_SUCCESS;
}

static cairo_status_t my_surface_get_font_options(cairo_surface_t *surface, cairo_font_options_t *options) {
    // Define your own code to get font options here
    return CAIRO_STATUS_SUCCESS;
}

static cairo_status_t my_surface_flush_image(cairo_surface_t *surface, cairo_surface_t *image_surface, cairo_rectangle_t *extents) {
    // Define your own code to flush an image here
    return CAIRO_STATUS_SUCCESS;
}

static const cairo_surface_backend_t my_surface_backend = {
    CAIRO_SURFACE_TYPE_CUSTOM,
    my_surface_finish,
    my_surface_create_similar,
    my_surface_map_to_image,
    my_surface_unmap_image,
    my_surface_acquire_source_image,
    my_surface_release_source_image,
    my_surface_acquire_dest_image,
    my_surface_release_dest_image,
    my_surface_clone_similar,
    my_surface_composite,
    my_surface_fill_rectangles,
    my_surface_fill_region,
    my_surface_set_device_offset,
    my_surface_get_device_offset,
    my_surface_set_fallback_resolution,
    my_surface_get_fallback_resolution,
    my_surface_copy_page,
    my_surface_show_page,
    my_surface_get_extents,
    my_surface_has_show_text_glyphs,
    my_surface_show_text_glyphs,
    my_surface_set_mime_data,
    my_surface_supports_mime_type,
    my_surface_snapshot,
    my_surface_copy_page,
    my_surface_show_page,
    my_surface_get_font_options,
    my_surface_flush,
    my_surface_flush_image,
    my_surface_create_observer,
    my_surface_create_similar_image,
    my_surface_map_to_image_surface,
    my_surface_unmap_image_surface
};

cairo_surface_t *my_surface_create() {
    MySurface *surface = malloc(sizeof(MySurface));
    surface->base.backend = &my_surface_backend;
    // Initialize your own properties here
    return &surface->base;
}

在上面的代码中，我们定义了一个MySurface结构体，它是cairo_surface_t的子类。我们还定义了一些函数，这些函数将用于绑定我们的自定义surface对象与Cairo库中的相关函数。

最后，我们定义了一个my_surface_create函数，该函数将创建并返回我们的自定义surface对象。

要使用自定义surface，只需将其传递给cairo_create函数即可：

cairo_surface_t *surface = my_surface_create();
cairo_t *cr = cairo_create(surface);

现在，我们已经成功地创建了一个自定义的Cairo绘图表面(surface)，并且可以使用它来进行绘制操作。