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rendering textures in clojure

2009

At its simplest, a texture is an image stretched across a shape. We can define a texture like so:

(def checkers (create-color-texture 128 128))

(draw-to-subsampled-texture
  checkers
  (fn [[x y] _]
    (if (xor (even? (int (/ x 16))) (even? (int (/ y 16))))
      [0.8 0.1 0.1 1]
      [0.1 0.1 0.1 1]))))

First we create a texture that is 128x128 pixels. Then we populate the texture using a function that returns a color for each individual pixel. We render the texture by associating two-dimensional coordinates in texture-space with each vertex. These coordinates are independent of any specific texture. To associate them with the texture we just defined, we must call bind-texture.

(defn textured-quad []
  (push-matrix
   (translate -0.5 -0.5 0.5)
   (normal 0 0 -1)
   (draw-quads
    (texture 1 1) (vertex 1 1 0)
    (texture 0 1) (vertex 0 1 0)
    (texture 0 0) (vertex 0 0 0)
    (texture 1 0) (vertex 1 0 0))))

(bind-texture checkers)
(textured-quad)

We can apply the same texture to multiple shapes. Wherever a textured quad is drawn, the texture that is currently bound will be drawn across it.

(defn textured-cube []

  ;; draw the four sides
  (dotimes [_ 4]
    (rotate 90 0 1 0)
    (textured-quad))

  ;; draw the top
  (rotate 90 1 0 0)
  (textured-quad)

  ;; draw the bottom
  (rotate 180 1 0 0)
  (textured-quad))

(bind-texture checkers)
(textured-cube)

This rendering of a cube can itself be made into a texture, which can be applied to another shape.

(def scene (create-texture 128 128))

(render-to-texture scene
  (with-projection (frustum-view 50 1 0.1 10)
    (textured-cube)))

Putting everything together, we get this:


These examples use the Penumbra library. Full code can be found in the /examples subdirectory.