image: add transmitPreEncodedImage method

Add a method that allows users of the library to pre-encode an image
using whichever base64 encoder they want (ie a simd encoder).

src/Vaxis.zig

@@ -717,38 +717,16 @@ pub fn translateMouse(self: Vaxis, mouse: Mouse) Mouse {
     return result;
 }
 
-pub fn transmitImage(
+/// Transmit an image which has been pre-base64 encoded
+pub fn transmitPreEncodedImage(
     self: *Vaxis,
-    alloc: std.mem.Allocator,
     tty: AnyWriter,
-    img: *zigimg.Image,
+    bytes: []const u8,
+    width: usize,
+    height: usize,
     format: Image.TransmitFormat,
 ) !Image {
-    if (!self.caps.kitty_graphics) return error.NoGraphicsCapability;
     defer self.next_img_id += 1;
-
-    var arena = std.heap.ArenaAllocator.init(alloc);
-    defer arena.deinit();
-
-    const buf = switch (format) {
-        .png => png: {
-            const png_buf = try arena.allocator().alloc(u8, img.imageByteSize());
-            const png = try img.writeToMemory(png_buf, .{ .png = .{} });
-            break :png png;
-        },
-        .rgb => rgb: {
-            try img.convert(.rgb24);
-            break :rgb img.rawBytes();
-        },
-        .rgba => rgba: {
-            try img.convert(.rgba32);
-            break :rgba img.rawBytes();
-        },
-    };
-
-    const b64_buf = try arena.allocator().alloc(u8, base64Encoder.calcSize(buf.len));
-    const encoded = base64Encoder.encode(b64_buf, buf);
-
     const id = self.next_img_id;
 
     const fmt: u8 = switch (format) {
@@ -757,41 +735,75 @@ pub fn transmitImage(
         .png => 100,
     };
 
-    if (encoded.len < 4096) {
+    if (bytes.len < 4096) {
         try tty.print(
             "\x1b_Gf={d},s={d},v={d},i={d};{s}\x1b\\",
             .{
                 fmt,
-                img.width,
-                img.height,
+                width,
+                height,
                 id,
-                encoded,
+                bytes,
             },
         );
     } else {
         var n: usize = 4096;
 
         try tty.print(
             "\x1b_Gf={d},s={d},v={d},i={d},m=1;{s}\x1b\\",
-            .{ fmt, img.width, img.height, id, encoded[0..n] },
+            .{ fmt, width, height, id, bytes[0..n] },
         );
-        while (n < encoded.len) : (n += 4096) {
-            const end: usize = @min(n + 4096, encoded.len);
-            const m: u2 = if (end == encoded.len) 0 else 1;
+        while (n < bytes.len) : (n += 4096) {
+            const end: usize = @min(n + 4096, bytes.len);
+            const m: u2 = if (end == bytes.len) 0 else 1;
             try tty.print(
                 "\x1b_Gm={d};{s}\x1b\\",
                 .{
                     m,
-                    encoded[n..end],
+                    bytes[n..end],
                 },
             );
         }
     }
     return .{
         .id = id,
-        .width = img.width,
-        .height = img.height,
+        .width = width,
+        .height = height,
+    };
+}
+
+pub fn transmitImage(
+    self: *Vaxis,
+    alloc: std.mem.Allocator,
+    tty: AnyWriter,
+    img: *zigimg.Image,
+    format: Image.TransmitFormat,
+) !Image {
+    if (!self.caps.kitty_graphics) return error.NoGraphicsCapability;
+
+    var arena = std.heap.ArenaAllocator.init(alloc);
+    defer arena.deinit();
+
+    const buf = switch (format) {
+        .png => png: {
+            const png_buf = try arena.allocator().alloc(u8, img.imageByteSize());
+            const png = try img.writeToMemory(png_buf, .{ .png = .{} });
+            break :png png;
+        },
+        .rgb => rgb: {
+            try img.convert(.rgb24);
+            break :rgb img.rawBytes();
+        },
+        .rgba => rgba: {
+            try img.convert(.rgba32);
+            break :rgba img.rawBytes();
+        },
     };
+
+    const b64_buf = try arena.allocator().alloc(u8, base64Encoder.calcSize(buf.len));
+    const encoded = base64Encoder.encode(b64_buf, buf);
+
+    return self.transmitPreEncodedImage(tty, encoded, img.width, img.height, format);
 }
 
 pub fn loadImage(