Create a Framebuffer and Write a PPM Image

Topic Overview

Framebuffers Store Raw Pixel Data

A framebuffer is a region of memory that stores pixel color values. Before GPUs existed, all rendering wrote colors directly into a framebuffer in system RAM. The concept remains central: your monitor displays whatever sits in the framebuffer.

Each pixel typically stores red, green, and blue as 8-bit channels (24 bits total). Some formats add an alpha channel for transparency. Every shader, texture upload, and swapchain present ultimately resolves to reading and writing these bytes.

The PPM Image Format

PPM (Portable Pixmap) is one of the simplest image formats. It stores pixels as plain text, ideal for learning and debugging:

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• P3: ASCII format (P6 is binary)
• Header: width, height, max color value (usually 255)
• Body: three integers per pixel (R G B)

For example, an 8x8 gradient from black at top-left to yellow at bottom-right uses red = (x * 255) / 7 and green = (y * 255) / 7.

For This Exercise

You will create an 8x8 RGB framebuffer, fill it with a red-green gradient, and print a valid PPM header plus pixel data to stdout. This task also asks for an ASCII preview using # and . characters. Our sandbox has no display, so stdout replaces writing a file. The row-major layout you build here is the same abstraction behind Linux /dev/fb0 and every software renderer in this subtrack.

Your Task

A software rasterizer draws into a framebuffer: a W×H array of RGB pixels, stored row by row. To see the result, you save it in the simplest image format there is, plain-text PPM (P3). Implement the framebuffer with a few drawing commands, and write it as P3.

Input

One command per line (# starts a comment line):

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Colour components are 0-255.

Output

write prints the P3 header P3, W H and 255, then one line per row. Each pixel is R G B, and pixels are separated by two spaces:

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Errors:

• size: W H (1-64)
• X: set a size first (any drawing before size)
• clear: R G B (0-255)
• pixel: X Y R G B, pixel (X, Y) is outside the WxH framebuffer
• rect: X Y W H R G B (W and H must be ≥ 0)
• unknown command X

Example

Input:

cCopy
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Output:

cCopy
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Requirements

1. Store pixels in one row-major buffer, where pixel (x, y) is at index y × W + x. Every later rasterizer task writes into this.
2. Clip rectangles pixel by pixel against the bounds, so a partly off-screen rectangle draws only its visible part.

Hidden tests cover a gradient, a rectangle hanging off every edge, an out-of-bounds pixel, a 1×1 image, and command errors.