jackdbd · jackdbd · Jan 23, 2021
diff --git a/build.zig b/build.zig
@@ -17,6 +17,7 @@ const EXAMPLES = [_][]const u8{
     "ellipse",
     "fill_and_stroke2",
     "fill_style",
+    "gaussian_blur",
     "glyphs",
     "gradient",
     "grid",

diff --git a/examples/gaussian_blur.zig b/examples/gaussian_blur.zig
@@ -0,0 +1,162 @@
+const std = @import("std");
+const exp = std.math.exp;
+const pi = std.math.pi;
+const log = std.log;
+const cairo = @import("cairo");
+const Format = cairo.image_surface.Format;
+const setBackground = @import("utils.zig").setBackground;
+
+/// https://www.cairographics.org/samples/image/
+fn image(cr: *cairo.Context) !void {
+    var surface = try cairo.Surface.createFromPng("data/romedalen.png");
+    defer surface.destroy();
+
+    const w = try surface.getWidth();
+    const h = try surface.getHeight();
+
+    cr.translate(128.0, 128.0);
+    cr.rotate(45 * pi / 180.0);
+    cr.scale(256.0 / @intToFloat(f64, w), 256.0 / @intToFloat(f64, h));
+    cr.translate(-0.5 * @intToFloat(f64, w), -0.5 * @intToFloat(f64, h));
+
+    cr.setSourceSurface(&surface, 0, 0);
+    cr.paint();
+}
+
+/// https://www.cairographics.org/cookbook/blur.c/
+fn blurImageSurface(allocator: *std.mem.Allocator, surface: *cairo.Surface, radius: u16) !void {
+    try cairo.checkSurfaceStatus(surface.surface);
+
+    const width = try surface.getWidth();
+    const height = try surface.getHeight();
+    const width_f64 = @intToFloat(f64, width);
+
+    // check that we are starting from a Cairo image surface
+    switch (cairo.image_surface.getFormat(surface.surface)) {
+        Format.A1 => {
+            return error.GaussianBlurNotImplementedForThisSurface;
+        },
+        Format.A8 => log.debug("Can blur but set width /= 4;", .{}),
+        Format.Argb32 => {
+            log.debug("Ok, can blur", .{});
+        },
+        Format.Rgb24 => {
+            log.debug("Ok, can blur", .{});
+        },
+        else => |format| {
+            log.debug("Format: {}", .{format});
+            return error.GaussianBlurNotImplementedForThisSurface;
+        },
+    }
+
+    var tmp = try cairo.image_surface.create(Format.Argb32, width, height);
+    // defer tmp.destroy();
+    try cairo.checkSurfaceStatus(tmp);
+
+    const src = try cairo.image_surface.getData(surface.surface);
+    // log.debug("src {}", .{src});
+    const src_stride = cairo.image_surface.getStride(surface.surface);
+    // log.debug("src_stride {}", .{src_stride});
+
+    const dest = try cairo.image_surface.getData(tmp);
+    const dest_stride = cairo.image_surface.getStride(tmp);
+
+    // build the gaussian kernel ///////////////////////////////////////////////
+    // TODO: add link to mathematical function
+    const size: usize = 17;
+    const half = @intToFloat(f64, size) / 2.0;
+    var kernel = std.ArrayList(f64).init(allocator);
+    var a: f64 = 0;
+    var i: usize = 0;
+    while (i < size) : (i += 1) {
+        const f = @intToFloat(f64, i) - half;
+        const coeff = exp(-f * f / 30.0) * 80.0;
+        try kernel.append(coeff);
+        a += coeff;
+    }
+
+    // blur the image //////////////////////////////////////////////////////////
+
+    // const s_addr = (@ptrToInt(src) + src_stride); // double-check the parentheses
+    // const s = @intToPtr([*]u32, s_addr);
+    // log.debug("s {}\n", .{@typeInfo(@TypeOf(s))});
+
+    // Horizontally blur from surface -> tmp
+    i = 0;
+    while (i < height) : (i += 1) {
+        // log.debug("height px {}/{}", .{i+1, height});
+        const s_addr = (@ptrToInt(src) + i * src_stride); // double-check the parentheses
+        const d_addr = (@ptrToInt(dest) + i * dest_stride);
+        const s = @intToPtr([*]u32, s_addr);
+        const d = @intToPtr([*]u32, d_addr);
+        // std.debug.print("s {}\n", .{@typeInfo(@TypeOf(s))});
+        var j: usize = 0;
+        while (j < width) : (j += 1) {
+            // log.debug("width px {}/{}", .{j+1, width});
+            if (radius < j and j < (width - radius)) {
+                // log.debug("d[j] = s[j]", .{});
+                d[j] = s[j];
+                continue;
+            } else {
+                // log.debug("ELSE", .{});
+                var x: f64 = 0;
+                var y: f64 = 0;
+                var z: f64 = 0;
+                var w: f64 = 0;
+
+                var k: usize = 0;
+                while (k < size) : (k += 1) {
+                    const k_f64 = @intToFloat(f64, k);
+                    const j_f64 = @intToFloat(f64, j);
+                    if ((j_f64 - half + k_f64 < 0) or (j_f64 - half + k_f64 >= width_f64)) {
+                        continue;
+                    } else {
+                        const idx = @floatToInt(usize, j_f64 - half + k_f64);
+                        const p = s[idx];
+                        // what are these things? What does this shifting mean?
+                        const px = @intToFloat(f64, (p >> 24) & 0xff);
+                        const py = @intToFloat(f64, (p >> 16) & 0xff);
+                        const pz = @intToFloat(f64, (p >> 8) & 0xff);
+                        const pw = @intToFloat(f64, (p >> 0) & 0xff);
+                        x += px * kernel.items[k];
+                        y += py * kernel.items[k];
+                        z += pz * kernel.items[k];
+                        w += pw * kernel.items[k];
+                    }
+                }
+                // d[j] = (x / a << 24) | (y / a << 16) | (z / a << 8) | w / a;
+                const a_u32 = @floatToInt(u32, a);
+                const cond1 = x / @intToFloat(f64, (a_u32 << 24));
+                const cond2 = y / @intToFloat(f64, (a_u32 << 16));
+                const cond3 = z / @intToFloat(f64, (a_u32 << 8));
+                const cond4 = w / a;
+                // d[j] = cond1 | cond2 | cond3 | cond4;
+            }
+        }
+    }
+
+    // TODO: Then vertically blur from tmp -> surface
+
+    cairo.c.cairo_surface_destroy(tmp);
+    cairo.c.cairo_surface_mark_dirty(surface.surface);
+}
+
+pub fn main() !void {
+    const width: u16 = 256;
+    const height: u16 = 256;
+    std.debug.print("gaussian_blur example ({}x{} px)\n", .{ width, height });
+
+    var surface = try cairo.Surface.image(width, height);
+    defer surface.destroy();
+
+    var cr = try cairo.Context.create(&surface);
+    defer cr.destroy();
+
+    setBackground(&cr);
+    try image(&cr);
+
+    const radius: u16 = 20;
+    try blurImageSurface(std.testing.allocator, &surface, radius);
+
+    _ = surface.writeToPng("examples/generated/gaussian_blur.png");
+}
diff --git a/src/cairo.zig b/src/cairo.zig
@@ -1,4 +1,5 @@
 //! zig-cairo: zig wrapper for Cairo
+const std = @import("std");
 
 // Export c to allow calling the C Cairo API.
 // For example, if you import zig-cairo with: