Where did the churn happen? the Changes Treemap¶

Once you've set a comparison database, the Changes Treemap shows where the change concentrated. It draws one box per changed entity, with box size and box colour each mapped to a change metric — so the big, hot boxes are the entities that moved the most.

Two treemaps, two questions

Understand has two treemaps. The Metrics Treemap (Metrics menu) shows your whole codebase sized/coloured by absolute metrics — see Where is my risky / complex code?. The Changes Treemap (Compare menu) shows only what changed between two versions, sized/coloured by change metrics. Reach for the Changes Treemap to answer "what did this release touch?"; the Metrics Treemap to answer "where is my risk right now?".

Open it¶

Set a comparison database first (Compare → Comparison Projects), then choose Compare → Changes Treemap. The menu item is disabled until a comparison database is set.

Only entities that differ between the two versions become boxes — added, removed, and changed entities. Everything unchanged is omitted, so the picture is pure signal about the delta.

The Metrics Treemap Options dialog for a Changes Treemap: Map metrics for Files, Group by Directory Structure, and Size and Color mapped to change metrics. — The options dialog opened by **Compare → Changes Treemap** — pick the change metrics for Size and Color, then **Generate Treemap**.

A generated Changes Treemap: only changed files appear as boxes, grouped by directory, with one file dominating the layout. — The result, sized by **Changed Lines**: one file (`cmGeneratorTarget.cxx`) carried a huge share of this release's churn.

Read it¶

Both size and colour are driven by change metrics you pick in the options dialog. The defaults:

Entity kind	Box size	Box colour
Files, Classes	Percent Changed (`PercentChanged`)	Change in Sum Cyclomatic (`DiffSumCyclomatic`)
Functions	Percent Changed (`PercentChanged`)	Change in Cyclomatic (`DiffCyclomatic`)

So by default a large box means a high proportion of the entity's lines changed, and a hot colour means its complexity moved a lot. The available metrics to map are the change metrics: New Lines (CountLineNew), Removed Lines (CountLineRemoved), Changed Lines (CountLineChanged), Percent Changed (PercentChanged), and the signed deltas DiffCountLine, DiffCountLineCode, DiffCountPath, and the cyclomatic diff.

It's a gradient, not a category

Colour is a continuous two-colour scale over the chosen metric — it is not a red/green add-vs-remove key. Added-vs-removed direction shows up in the signed delta metrics (a negative DiffCountLine means the entity shrank). Use the Changed Entities Locator or the diff when you need the discrete Added/Changed/Removed status.

Change what it maps¶

The Changes Treemap uses the same options dialog as the Metrics Treemap, so the controls are familiar:

Map metrics for: — the entity kind to show (files, classes, functions).
Map Size to: / Map Color to: — the change metrics driving box area and colour.
Group by: — nest boxes by an architecture.
Min Color / Max Color and Use logarithmic Scale — tune the colour scale (log scale pulls extreme outliers into view).

Press Generate Treemap to apply. Click a box to open the side-by-side comparison of that entity's old and new source.