133 lines
4.5 KiB
Markdown
133 lines
4.5 KiB
Markdown
Skia's Stable C API
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===================
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<div style="text-align:center">
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<strong>EXPERIMENTAL EXPERIMENTAL EXPERIMENTAL EXPERIMENTAL<br>
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DO NOT USE — FOR INTERNAL TESTING ONLY</strong>
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</div>
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Several issues hinder the development of a stable ABI (application
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binary interface) for Skia:
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1. Skia's C++ API changes a lot from version to version. Skia's two
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largest clients, Android and Chrome, are kept up to date by the
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Skia team, but that can not happen for every client.
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2. Skia's headers will only match the compiled skia libraries if
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configured identically.
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To mitigate these two issues, Skia is experimenting with the
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introduction of a C API. This will change more slowly than the C++
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interface and, once API version 1.0.0 is announced,
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backwards-incompatable changes will be avoided whenever possible.
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Here is an example program that uses the C api. To try it out, get the file
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[`skia-c-example.c`](./skia-c-example.c).
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<!--?prettify lang=c?-->
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#include <stdio.h>
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#include "sk_data.h"
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#include "sk_image.h"
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#include "sk_canvas.h"
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#include "sk_surface.h"
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#include "sk_paint.h"
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#include "sk_path.h"
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static sk_surface_t* make_surface(int32_t w, int32_t h) {
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sk_imageinfo_t info;
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info.width = w;
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info.height = h;
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info.colorType = sk_colortype_get_default_8888();
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info.alphaType = PREMUL_SK_ALPHATYPE;
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return sk_surface_new_raster(&info, NULL);
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}
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static void emit_png(const char* path, sk_surface_t* surface) {
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sk_image_t* image = sk_surface_new_image_snapshot(surface);
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sk_data_t* data = sk_image_encode(image);
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sk_image_unref(image);
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FILE* f = fopen(path, "wb");
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fwrite(sk_data_get_data(data), sk_data_get_size(data), 1, f);
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fclose(f);
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sk_data_unref(data);
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}
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void draw(sk_canvas_t* canvas) {
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sk_paint_t* fill = sk_paint_new();
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sk_paint_set_color(fill, sk_color_set_argb(0xFF, 0x00, 0x00, 0xFF));
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sk_canvas_draw_paint(canvas, fill);
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sk_paint_set_color(fill, sk_color_set_argb(0xFF, 0x00, 0xFF, 0xFF));
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sk_rect_t rect;
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rect.left = 100.0f;
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rect.top = 100.0f;
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rect.right = 540.0f;
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rect.bottom = 380.0f;
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sk_canvas_draw_rect(canvas, &rect, fill);
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sk_paint_t* stroke = sk_paint_new();
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sk_paint_set_color(stroke, sk_color_set_argb(0xFF, 0xFF, 0x00, 0x00));
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sk_paint_set_antialias(stroke, true);
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sk_paint_set_stroke(stroke, true);
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sk_paint_set_stroke_width(stroke, 5.0f);
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sk_path_t* path = sk_path_new();
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sk_path_move_to(path, 50.0f, 50.0f);
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sk_path_line_to(path, 590.0f, 50.0f);
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sk_path_cubic_to(path, -490.0f, 50.0f, 1130.0f, 430.0f, 50.0f, 430.0f);
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sk_path_line_to(path, 590.0f, 430.0f);
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sk_canvas_draw_path(canvas, path, stroke);
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sk_paint_set_color(fill, sk_color_set_argb(0x80, 0x00, 0xFF, 0x00));
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sk_rect_t rect2;
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rect2.left = 120.0f;
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rect2.top = 120.0f;
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rect2.right = 520.0f;
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rect2.bottom = 360.0f;
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sk_canvas_draw_oval(canvas, &rect2, fill);
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sk_path_delete(path);
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sk_paint_delete(stroke);
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sk_paint_delete(fill);
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}
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int main() {
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sk_surface_t* surface = make_surface(640, 480);
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sk_canvas_t* canvas = sk_surface_get_canvas(surface);
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draw(canvas);
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emit_png("skia-c-example.png", surface);
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sk_surface_unref(surface);
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return 0;
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}
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<a href="https://fiddle.skia.org/c/6c6c01438d9c3d80e9c22e606359432e"><img src="https://fiddle.skia.org/i/6c6c01438d9c3d80e9c22e606359432e_raster.png" alt=""></a>
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Cmake example
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-------------
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The following proof-of-concept workflow currently works on MacOS and
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Ubuntu and depends on a C/C++ compiler, git, and cmake:
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1. Aquire, compile, and install Skia as a shared library:
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<!--?prettify lang=sh?-->
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prefix="$HOME"
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cd $(mktemp -d /tmp/skiaXXXX)
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git clone 'https://skia.googlesource.com/skia'
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cmake -DCMAKE_INSTALL_PREFIX:PATH="$prefix" skia/cmake
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cmake --build . --target skia
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cmake --build . --target install
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2. Compile, link, and run the example program:
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<!--?prettify lang=sh?-->
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cc -o skia-c-example -I "$prefix/include" \
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skia/experimental/c-api-example/skia-c-example.c \
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"$prefix"/lib/libskia.* -Wl,-rpath -Wl,"$prefix/lib"
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./skia-c-example
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[ $(uname) = Darwin ] && open skia-c-example.png
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[ $(uname) = Linux ] && xdg-open skia-c-example.png
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