правильное определение видимой области

src/render/CpuRenderEngine.zig

@@ -34,19 +34,7 @@ pub fn exampleReset(self: *CpuRenderEngine) void {
     self.gradient_end = Color.PMA{ .r = random.int(u8), .g = random.int(u8), .b = random.int(u8), .a = 255 };
 }
 
-pub fn example(self: CpuRenderEngine, canvas_size: ImageSize, visible_rect: ImageRect) !?dvui.Texture {
-    const full_w = canvas_size.w;
-    const full_h = canvas_size.h;
-
-    const width = visible_rect.w;
-    const height = visible_rect.h;
-
-    // Выделить буфер пиксельных данных
-    const pixels = try self._allocator.alloc(Color.PMA, @as(usize, width) * height);
-    defer self._allocator.free(pixels);
-
-    std.debug.print("w={any}, fw={any};\th={any}, fh={any}\n", .{ width, full_w, height, full_h });
-
+fn renderGradient(self: CpuRenderEngine, pixels: []Color.PMA, width: u32, height: u32, full_w: u32, full_h: u32, visible_rect: ImageRect) void {
     var y: u32 = 0;
     while (y < height) : (y += 1) {
         var x: u32 = 0;
@@ -70,6 +58,52 @@ pub fn example(self: CpuRenderEngine, canvas_size: ImageSize, visible_rect: Imag
             pixels[y * width + x] = .{ .r = r, .g = g, .b = b, .a = 255 };
         }
     }
+}
+
+fn renderSquares(self: CpuRenderEngine, pixels: []Color.PMA, canvas_size: ImageSize, visible_rect: ImageRect) void {
+    _ = self;
+
+    const squares_num = 5;
+    const thikness: u32 = @intFromFloat(@as(f32, @floatFromInt(canvas_size.w + canvas_size.h)) / 2 * 0.03);
+    const squares_sum_height = canvas_size.h - thikness * (squares_num + 1);
+    const square_height = squares_sum_height / squares_num;
+
+    var y: u32 = 0;
+    while (y < visible_rect.h) {
+        const canvas_y = y + visible_rect.y;
+        var start_line_index = canvas_y / square_height;
+
+        start_line_index = start_line_index * square_height + thikness * (if (start_line_index > 0) start_line_index - 1 else 0);
+        const draw_line = canvas_y < start_line_index + thikness and canvas_y >= start_line_index;
+        if (draw_line) {
+            var x: u32 = 0;
+            while (x < visible_rect.w) {
+                pixels[y * visible_rect.w + x] = .{ .r = 255, .b = 0, .g = 0, .a = 255 };
+
+                x += 1;
+            }
+        }
+        y += 1;
+    }
+}
+
+pub fn example(self: CpuRenderEngine, canvas_size: ImageSize, visible_rect: ImageRect) !?dvui.Texture {
+    const full_w = canvas_size.w;
+    const full_h = canvas_size.h;
+
+    const width = visible_rect.w;
+    const height = visible_rect.h;
+
+    // Выделить буфер пиксельных данных
+    const pixels = try self._allocator.alloc(Color.PMA, @as(usize, width) * height);
+    defer self._allocator.free(pixels);
+
+    std.debug.print("w={any}, fw={any};\th={any}, fh={any}\n", .{ width, full_w, height, full_h });
+
+    switch (self.type) {
+        .Gradient => self.renderGradient(pixels, width, height, full_w, full_h, visible_rect),
+        .Squares => self.renderSquares(pixels, canvas_size, visible_rect),
+    }
 
     return try dvui.textureCreate(pixels, width, height, .nearest);
 }