C API: Add SK_API, also documentation of an example.

experimental/c-api-example/skia-c-example.c

Index: experimental/c-api-example/skia-c-example.c
diff --git a/experimental/c-api-example/skia-c-example.c b/experimental/c-api-example/skia-c-example.c
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+++ b/experimental/c-api-example/skia-c-example.c
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+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#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_path_t* path = sk_path_new();
+
+    sk_path_move_to(path, 50.0f, 50.0f);
+    sk_path_line_to(path, 590.0f, 50.0f);
+    sk_path_cubic_to(path, -490.0f, 50.0f, 1130.0f, 430.0f, 50.0f, 430.0f);
+    sk_path_line_to(path, 590.0f, 430.0f);
+    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_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;
+}