rendering: add bounded size hint

Provides a new size-hint mechanism for rendering, `bounded`.  A bounded
size hint specifies a limit for both width and height and then renders the
maximum size that fits within these limits while also maintaining the
aspect ratio.

This option is exposed in `tvg-render` via the:

    --bounded <width>x<height>

command line option.

docs/sdk-readme.txt

@@ -43,6 +43,7 @@ Tools:
       -g, --geometry         Specifies the output geometry of the image. Has the format <width>x<height>.
           --width <width>    Specifies the output width to be <width>. Height will be derived via aspect ratio.
           --height <height>  Specifies the output height to be <height>. Width will be derived via aspect ratio.
+          --bounded <geom>   Output's maximum size within the given <width>x<height> that maintains the aspect ratio.
       -s, --super-sampling   Sets the super-sampling size for the image. Use 1 for no super sampling and 16 for very high quality.
       -a, --anti-alias       Sets the super-sampling size to 4. This is usually decent enough for most images.
 

src/lib/rendering.zig

@@ -57,6 +57,9 @@ pub fn renderStream(
             .width = (height * parser.header.width) / parser.header.height,
             .height = height,
         },
+        .bounded => |bounds| calcBoundedSize(
+            bounds, parser.header.width, parser.header.height
+        ),
     };
 
     const super_scale: u32 = if (anti_alias) |factor|
@@ -226,8 +229,25 @@ pub const SizeHint = union(enum) {
     width: u32,
     height: u32,
     size: Size,
+    /// The maximum size that maintains the aspect ratio and fits within the given bounds
+    bounded: Size,
 };
 
+fn calcBoundedSize(bounds: Size, width: u32, height: u32) Size {
+    const width_f32: f32 = @floatFromInt(width);
+    const height_f32: f32 = @floatFromInt(height);
+    const width_mult = @as(f32, @floatFromInt(bounds.width)) / width_f32;
+    const height_mult = @as(f32, @floatFromInt(bounds.height)) / height_f32;
+    if (width_mult >= height_mult) return .{
+        .width = @intFromFloat(@trunc(width_f32 * height_mult)),
+        .height = bounds.height,
+    };
+    return .{
+        .width = bounds.width,
+        .height = @intFromFloat(@trunc(height_f32 * width_mult)),
+    };
+}
+
 pub const Size = struct {
     width: u32,
     height: u32,

src/tools/render.zig

@@ -14,6 +14,7 @@ fn printUsage(stream: anytype) !void {
         \\  -g, --geometry <geom>  Specifies the output geometry of the image. Has the format <width>x<height>.
         \\      --width <width>    Specifies the output width to be <width>. Height will be derived via aspect ratio.
         \\      --height <height>  Specifies the output height to be <height>. Width will be derived via aspect ratio.
+        \\      --bounded <geom>   Output's maximum size within the given <width>x<height> that maintains the aspect ratio.
         \\  -s, --super-sampling   Sets the super-sampling size for the image. Use 1 for no super sampling and 16 for very high quality.
         \\  -a, --anti-alias       Sets the super-sampling size to 4. This is usually decent enough for most images.
         \\
@@ -28,6 +29,10 @@ const CliOptions = struct {
     geometry: ?Geometry = null,
     width: ?u32 = null,
     height: ?u32 = null,
+    bounded: ?Geometry = null,
+
+    max_width: ?u32 = null,
+    max_height: ?u32 = null,
 
     @"anti-alias": bool = false,
     @"super-sampling": ?u32 = null,
@@ -69,8 +74,9 @@ pub fn main() !u8 {
     if (cli.options.width != null) cnt += 1;
     if (cli.options.height != null) cnt += 1;
     if (cli.options.geometry != null) cnt += 1;
+    if (cli.options.bounded != null) cnt += 1;
     if (cnt > 1) {
-        try stderr.writeAll("--width, --height and --geometry are mutual exclusive!\n");
+        try stderr.writeAll("--width, --height, --geometry and --bounded are mutually exclusive!\n");
         try printUsage(stderr);
         return 1;
     }
@@ -118,6 +124,8 @@ pub fn main() !u8 {
             tvg.rendering.SizeHint{ .height = height }
         else if (cli.options.geometry) |geom|
             tvg.rendering.SizeHint{ .size = tvg.rendering.Size{ .width = geom.width, .height = geom.height } }
+        else if (cli.options.bounded) |b|
+            tvg.rendering.SizeHint{ .bounded = .{ .width = b.width, .height = b.height } }
         else
             .inherit,
         @enumFromInt(super_scale),