Make a Proportional Thumbnail

Make a Proportional Thumbnail

Product pictures reach your extension as Base64 text — an API payload here, an imported catalog there — and the web shop wants a small preview for its item list. Squeezing a 4000-pixel photo into a 64-pixel tile is the browser's problem; producing a proportionally shrunk thumbnail, and refusing payloads that only pretend to be images, is yours. The good news: the System Application ships an Image codeunit that loads Base64, reads pixel sizes, resizes, and encodes back — your job is wiring it up and getting the proportional math and its boundaries exactly right.

Requirements

Create a codeunit named "Thumbnail Generator" with two public procedures:

procedure GetDimensions(ImageBase64: Text; var Width: Integer; var Height: Integer)
procedure CreateThumbnail(ImageBase64: Text; MaxDimension: Integer): Text

Rules:

1. GetDimensions loads the image encoded in ImageBase64 and returns its pixel width and height through the two var parameters — width is the horizontal side, height the vertical one — don't swap them.
2. CreateThumbnail returns the picture as Base64 again, scaled down so that neither side exceeds MaxDimension pixels:
   • if width and height both already fit within MaxDimension, the picture keeps its size — never scale up;
   • otherwise the longer side becomes exactly MaxDimension and the other side is multiplied by the same factor (MaxDimension divided by the longer side), rounded to the nearest whole pixel — an exact half rounds up, so 25.6 becomes 26 and 7.5 becomes 8;
   • a side that would round down to 0 becomes 1 pixel instead — no side of the thumbnail is ever smaller than 1;
   • a square picture larger than the limit becomes exactly MaxDimension × MaxDimension.
3. Input that cannot be loaded as an image — text that isn't Base64 at all, or perfectly valid Base64 hiding bytes that aren't a picture — must make the call fail with an error, in both procedures. Any error text is fine: the tests only check that an error is raised, not what it says.
4. The tests always feed PNG images and a MaxDimension of at least 1, and the thumbnail they get back must still be a PNG. The returned Base64 does not have to be byte-identical to the input — the tests judge the thumbnail only by its decoded width, height, and format.

Pick object IDs in the range 50100–50199, and reference other objects by name, never by ID.

What the tests check

The grading tests decode the Base64 you return and measure it: a 100×40 PNG with a limit of 50 must come back as 50×20 and a 40×100 PNG as 20×50, an 80×80 PNG with a limit of 32 must become 32×32, and one test picks a random limit and recomputes the expected shorter side itself — hardcoding the examples won't survive it. Rounding is pinned at three spots: 100×40 with a limit of 64 must give 64×26, 20×10 with a limit of 15 must give 15×8, and 100×40 with a limit of 41 must give 41×16 — a fraction below one half (16.4) rounds down, so always rounding up fails here. A 20×10 PNG is returned unchanged in size both for a limit of 64 and for a limit of exactly 20, and a 100×2 PNG with a limit of 10 must become 10×1 — not fail, and not 10×0. GetDimensions is checked on a landscape and a portrait fixture, every thumbnail the tests get back is reloaded and must still decode as a PNG, and both procedures are fed plain prose and Base64-encoded prose and must raise an error each time.

Learn More

• Image codeunit (System Application) — the full toolbox this task runs on: FromBase64, GetWidth, GetHeight, Resize, GetFormat, ToBase64.
• Image Format enum (System Application) — the format values GetFormat can report, Png among them.
• System.Round method — precision and direction arguments; the default '=' direction rounds halves up, exactly what the shorter side needs.
• Base64 Convert codeunit (System Application) — what Base64 encoding is in BC terms, useful background even though Image handles it for you here.