The design law of a slide page

Every slide in this runtime was drawn under a long set of rules, the canvas, the height table, the type scale, the spacing standards. The generator that drew the page had all of them in front of it. When you patch one element, you have the page's numbers and nothing else, and the rules are the only way to tell a repair from a dent.

This is that rule set, restated for editing. It is about the page, not the process: which numbers a change has to stay consistent with, and which fields actually reach the screen.

The canvas you are editing inside

The canvas is 1000 × 562.5. All elements respect a 50px margin, so the live area is left ∈ [50, 950], top ∈ [50, 512.5], and an element's right edge (left + width) stays ≤ 950, its bottom edge ≤ 512.5.

The page's own alignment grid, which existing elements are already on:

• Left-aligned content sits at left = 60 or left = 80.
• Centred content is left = (1000 - width) / 2, recomputed, never guessed.
• Right-aligned content is left = 1000 - width - 60.

Changing width on centred content changes left too, and they are two separate writes. Read the neighbours' boxes first and land on the column they are already using; a lone element 8px off the shared left edge reads as a mistake even though nothing overflows.

There is no alignment operation. Every position is an explicit number you write to that element's own left / top / width / height, one path per call, computed from the neighbours you read. Aligning a row means giving each element the number the row already uses, not asking the page to tidy itself.

Text is sized by table, not by eye

A text element has 10px padding on all four sides, so its usable area is (width - 20) × (height - 20), and heights come from one table (line-height 1.5, padding included):