Several issues hinder the development of a stable ABI (application binary interface) for Skia:
To mitigate these two issues, Skia is experimenting with the introduction of a C API. This will change more slowly than the C++ interface and, once API version 1.0.0 is announced, backwards-incompatable changes will be avoided whenever possible.
Here is an example program that uses the C api. To try it out, get the file skia-c-example.c
.
#include <stdio.h> #include "sk_data.h" #include "sk_image.h" #include "sk_canvas.h" #include "sk_surface.h" #include "sk_paint.h" #include "sk_path.h" static sk_surface_t* make_surface(int32_t w, int32_t h) { sk_imageinfo_t info; info.width = w; info.height = h; info.colorType = sk_colortype_get_default_8888(); info.alphaType = PREMUL_SK_ALPHATYPE; return sk_surface_new_raster(&info, NULL); } static void emit_png(const char* path, sk_surface_t* surface) { sk_image_t* image = sk_surface_new_image_snapshot(surface); sk_data_t* data = sk_image_encode(image); sk_image_unref(image); FILE* f = fopen(path, "wb"); fwrite(sk_data_get_data(data), sk_data_get_size(data), 1, f); fclose(f); sk_data_unref(data); } void draw(sk_canvas_t* canvas) { sk_paint_t* fill = sk_paint_new(); sk_paint_set_color(fill, sk_color_set_argb(0xFF, 0x00, 0x00, 0xFF)); sk_canvas_draw_paint(canvas, fill); sk_paint_set_color(fill, sk_color_set_argb(0xFF, 0x00, 0xFF, 0xFF)); sk_rect_t rect; rect.left = 100.0f; rect.top = 100.0f; rect.right = 540.0f; rect.bottom = 380.0f; sk_canvas_draw_rect(canvas, &rect, fill); sk_paint_t* stroke = sk_paint_new(); sk_paint_set_color(stroke, sk_color_set_argb(0xFF, 0xFF, 0x00, 0x00)); sk_paint_set_antialias(stroke, true); sk_paint_set_stroke(stroke, true); sk_paint_set_stroke_width(stroke, 5.0f); sk_pathbuilder_t* path_builder = sk_pathbuilder_new(); sk_pathbuilder_move_to(path_builder, 50.0f, 50.0f); sk_pathbuilder_line_to(path_builder, 590.0f, 50.0f); sk_pathbuilder_cubic_to(path_builder, -490.0f, 50.0f, 1130.0f, 430.0f, 50.0f, 430.0f); sk_pathbuilder_line_to(path_builder, 590.0f, 430.0f); sk_path_t* path = sk_pathbuilder_detach_path(path_builder); sk_canvas_draw_path(canvas, path, stroke); sk_paint_set_color(fill, sk_color_set_argb(0x80, 0x00, 0xFF, 0x00)); sk_rect_t rect2; rect2.left = 120.0f; rect2.top = 120.0f; rect2.right = 520.0f; rect2.bottom = 360.0f; sk_canvas_draw_oval(canvas, &rect2, fill); sk_pathbuilder_delete(path_builder); sk_path_delete(path); sk_paint_delete(stroke); sk_paint_delete(fill); } int main() { sk_surface_t* surface = make_surface(640, 480); sk_canvas_t* canvas = sk_surface_get_canvas(surface); draw(canvas); emit_png("skia-c-example.png", surface); sk_surface_unref(surface); return 0; }
The following proof-of-concept workflow currently works on MacOS and Ubuntu.
Compile Skia as a shared library:
cd ...../skia bin/sync gn gen out/Shared --args='is_official_build=true is_component_build=true' ninja -C out/Shared SKIA_LIB_DIR="${PWD}/out/Shared"
Compile, link, and run the example program:
cc -o skia-c-example -I include/c \ experimental/c-api-example/skia-c-example.c \ "$SKIA_LIB_DIR"/libskia.* -Wl,-rpath -Wl,"$SKIA_LIB_DIR" ./skia-c-example bin/sysopen skia-c-example.png