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CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Project Overview

Sketch is a Common Lisp framework for creative coding and visual design, inspired by Processing. It provides an immediate-mode graphics API built on SDL2 and OpenGL 3.3+.

Build and Run Commands

;; Load the library (from REPL with Quicklisp)
(ql:quickload :sketch)

;; Load and run examples
(ql:quickload :sketch-examples)
(make-instance 'sketch-examples:hello-world)

;; Run tests
(ql:quickload :sketch-tests)
(sketch-tests:run-tests)

Architecture

Core Abstractions

  • defsketch macro (src/sketch.lisp): Main entry point. Creates a class that inherits from sketch with a drawing body that runs at ~60fps. The body is Lisp code with direct calls to drawing functions.

  • Environment (src/environment.lisp): The env struct holds all rendering state (pen, font, matrix stack, textures). Accessed via *env* special variable during drawing.

  • Pen (src/pen.lisp): Drawing attributes (stroke color, fill color, weight, curve-steps, winding-rule). Use make-pen and with-pen macro.

  • Transforms (src/transforms.lisp): Matrix-based 2D transforms (translate, rotate, scale) with stack operations (push-matrix, pop-matrix). Scoped versions use with-translate, with-rotate, with-scale.

Module Organization

Module Purpose
sketch.lisp Sketch class, defsketch macro, window lifecycle
shapes.lisp Primitive shapes: rect, circle, ellipse, line, polygon, bezier, ngon
color.lisp Color models (RGB/HSB), color constants (+red+, +blue+, etc.), color filters
controllers.lisp Input event handling: on-click, on-hover, on-key, on-text
resources.lisp Resource loading/caching for images and fonts
canvas.lisp Pixel-level drawing surface
entities.lisp defentity macro for reusable drawable objects with input handling

Drawing Model

Procedural/non-retained: drawing functions are called directly in the sketch body, which re-executes every frame. No scene graph - but internally, geometry is batched into vertex buffers before rendering (modern OpenGL with VAOs/VBOs). Example:

(defsketch my-sketch
    ((x 0))
  (incf x)
  (circle x 200 50))

Input Handling

Define methods on your sketch class:

(defmethod on-click ((instance my-sketch) x y) ...)
(defmethod on-key ((instance my-sketch) key state) ...)
(defmethod on-hover ((instance my-sketch) x y) ...)

Key Patterns

  • Slot bindings in defsketch are available as lexical variables in the body
  • setup generic function runs once on sketch start/restart
  • (copy-pixels t) prevents screen clearing between frames
  • y-axis option (:down default, or :up) controls coordinate system orientation
  • Resources are auto-cached; call load-resource in body without performance penalty

Foreign Dependencies

SDL2, SDL2_IMAGE, SDL2_TTF, libffi, OpenGL 3.3+

Supported Lisp Implementations

SBCL (Linux), CCL (macOS recommended due to GUI threading). See README.org for platform-specific notes.