UGTK / Toolkit / Ui Module / Raw Image Preserve Aspect Completed

Raw Image Preserve Aspect

Summary

Mn_RawImagePreserveAspect is a RawImage subclass that gives it the Preserve Aspect toggle Unity only ships on Image. It letterboxes the texture inside the RectTransform — without touching the RectTransform itself — while still honouring uvRect and supporting SetNativeSize().

It is what you need whenever the texture is not an imported sprite: a RenderTexture, a webcam feed, a downloaded image, a Texture2D built in code. Those all have to go through RawImage, and RawImage stretches by default.

Modules Dependencies

None on the UGTK side. It only relies on Unity UI (UnityEngine.UI.RawImage).

Setup

Drop the RawImage prefab under a Canvas — a RectTransform already carrying Mn_RawImagePreserveAspect with Preserve Aspect on:

Or add the component from UI ▸ Raw Image (Preserve Aspect). On an existing RawImage you cannot just add the component — it is a RawImage — so remove the old one and add this instead, then re-assign the texture.

How To Use

Assign Texture as on any RawImage.
Preserve Aspect (on by default): the texture is fitted inside the rect with letterboxing (black bars top/bottom or left/right, depending on which side is in excess). Turn it off and it stretches to fill, exactly like a stock RawImage.
UV Rect keeps working: cropping and tiling behave as usual, applied to the fitted quad.
Set Native Size() resizes the RectTransform to the texture's pixel size, like Image does.

var raw = GetComponent<Mn_RawImagePreserveAspect>();
raw.texture = myRenderTexture;
raw.preserveAspect = true;   // rebuilds the mesh straight away
raw.SetNativeSize();         // RectTransform = texture pixel size

Good to know:

The RectTransform never moves. The fit happens in the generated mesh, so layout groups, anchors and any sibling UI keep working on the full rect. The "empty" band is just not drawn — it is transparent, not black: put a background Image behind it if you want visible bars.
The raycast target is still the whole rect. Clicks in the letterboxed band are captured by this graphic even though nothing is drawn there. Turn Raycast Target off, or shrink the rect, if the band must be click-through.
SetNativeSize() collapses the anchors (anchorMax = anchorMin) before resizing, exactly like Image.SetNativeSize does: a stretched RawImage stops being stretched after calling it.
A RenderTexture that changes size re-fits by itself at the next mesh rebuild, but changing texture from code does not always mark the vertices dirty: call SetVerticesDirty() if you see a stale fit.
With no texture assigned the component draws a plain quad on the whole rect, tinted with color — the usual RawImage placeholder.

Testing Scene

Open Debug/RawImagePreserveAspectSceneTest.unity: the same texture is shown in rects of different proportions, with and without Preserve Aspect, so the letterboxing is immediately visible.

Technical Info

Path	Content
`Scripts/Runtime/Mn_RawImagePreserveAspect.cs`	The component: `OnPopulateMesh` override that builds the fitted quad, `GetDrawingDimensions` (min-fit letterbox), `SetNativeSize` override
`Prefabs/RawImage.prefab`	RawImage with the component already attached
`Debug/RawImagePreserveAspectSceneTest.unity`	Test scene

API: preserveAspect (bool property, rebuilds the mesh on change), SetNativeSize(), plus everything inherited from RawImage (texture, uvRect, color, material, …).

The maths: from the rect ratio and the texture ratio, the wider of the two dimensions is padded by (excess / 2) on both sides — the same min-fit Image uses, which is why the two components look identical side by side.