Render Overlapping Rectangles on an ASCII Canvas

Implement render_canvas(width, height, rectangles). The canvas initially contains spaces and is returned as a list of height strings, each of length width.

Each rectangle is (x, y, w, h, border_char, fill_char), where (x, y) is its upper-left corner, w is its width, and h is its height. Draw the outermost cells with border_char and interior cells with fill_char. Coordinates may place part or all of a rectangle outside the canvas; clip safely. Rectangles are drawn in input order, so later rectangles overwrite earlier pixels wherever they overlap.

Constraints

• 0 <= width, height <= 1000
• 1 <= w, h <= 1000
• x and y may be negative.
• border_char and fill_char are single printable characters.
• The total canvas area is at most 10^6 cells.

Example

For a 5 by 4 canvas and rectangle (1, 1, 3, 2, '#', '.'), return:

     
 ### 
 ### 
     

A one-cell-wide or one-cell-high rectangle consists entirely of border cells.

Clarifications

Canvas coordinates use zero-based columns and rows. Preserve trailing spaces in every returned row. Explain how clipping prevents invalid indexing without changing whether a visible cell is a border or interior cell of the original rectangle.

Hints

Intersect each rectangle's coordinate range with the canvas before visiting pixels, but compute border status in the rectangle's original coordinates.

Extensions

• Return only changed regions for a very large sparse canvas.
• Support transparency or z-indexes.
• Add tests for total clipping, corner clipping, thin rectangles, and overwrite order.

Render Overlapping Rectangles on an ASCII Canvas

Implement render_canvas(width, height, rectangles). Create a blank canvas and return it as a list of height strings, each containing exactly width cells. Each rectangle is (x, y, w, h, border_char, fill_char), with (x, y) as its upper-left corner. Draw cells on the rectangle's original outer edge with border_char and its interior with fill_char. Clip any portion outside the canvas safely, but determine border versus interior from the original rectangle coordinates. Process rectangles in input order so every later rectangle overwrites earlier pixels where they overlap. A one-cell-wide or one-cell-high rectangle consists entirely of border cells, and trailing spaces in every returned row must be preserved.

Hints

1. Intersect each rectangle's coordinate range with the canvas before visiting pixels, but compute border status in the rectangle's original coordinates.

Approach

Allocate the height-by-width canvas with one space per cell. For each rectangle, intersect its half-open column range [x, x + w) and row range [y, y + h) with the canvas ranges. If either intersection is empty, the rectangle performs no writes. Visit only cells in the intersection. A visited cell is on the rectangle's border exactly when its column is x or x + w - 1, or its row is y or y + h - 1; these comparisons deliberately use the original rectangle bounds rather than the clipped bounds. Write border_char for those cells and fill_char otherwise. Because rectangles are processed sequentially and each write replaces the current cell, later rectangles have the required overwrite priority. Finally join each row's cells without trimming, which preserves both leading and trailing spaces. The clipping intersection guarantees every visited row and column is a valid canvas index, while the original-boundary test guarantees clipping cannot turn an interior cell into a false border.

• Time complexity: O(width * height + sum of the visible intersection areas of all rectangles)
• Space complexity: O(width * height)