buffers.org

Contents

• Read-back float buffer
  • Complete namespace definition

Read-back float buffer

#define FLOAT_MAX 1.70141184e38
#define FLOAT_MIN 1.17549435e-38

lowp vec4 packFloat(highp float v) {
  highp float av = abs(v);

  //Handle special cases
  if(av < FLOAT_MIN) {
    return vec4(0.0, 0.0, 0.0, 0.0);
  } else if(v > FLOAT_MAX) {
    return vec4(127.0, 128.0, 0.0, 0.0) / 255.0;
  } else if(v < -FLOAT_MAX) {
    return vec4(255.0, 128.0, 0.0, 0.0) / 255.0;
  }

  highp vec4 c = vec4(0);

  //Compute exponent and mantissa
  highp float e = floor(log2(av));
  highp float m = av * pow(2.0, -e) - 1.0;

  //Unpack mantissa
  c[1] = floor(128.0 * m);
  m -= c[1] / 128.0;
  c[2] = floor(32768.0 * m);
  m -= c[2] / 32768.0;
  c[3] = floor(8388608.0 * m);

  //Unpack exponent
  highp float ebias = e + 127.0;
  c[0] = floor(ebias / 2.0);
  ebias -= c[0] * 2.0;
  c[1] += floor(ebias) * 128.0;

  //Unpack sign bit
  c[0] += 128.0 * step(0.0, -v);

  //Scale back to range
  return c / 255.0;
}

(def ^:private uint-buf #?(:clj (ByteBuffer/allocate 4) :cljs (js/Uint8Array. 4)))
(def ^:private float-buf #?(:clj (.asFloatBuffer uint-buf) :cljs (js/Float32Array. uint-buf)))

#?(:clj
   (defn unpack-float
     [a b c d]
     (.put ^ByteBuffer uint-buf 0 (unchecked-byte a))
     (.put ^ByteBuffer uint-buf 1 (unchecked-byte b))
     (.put ^ByteBuffer uint-buf 2 (unchecked-byte c))
     (.put ^ByteBuffer uint-buf 3 (unchecked-byte d))
     (.get ^FloatBuffer float-buf 0))
   :cljs
   (defn unpack-float
     [a b c d]
     (aset uint-buf 0 a)
     (aset uint-buf 1 b)
     (aset uint-buf 2 c)
     (aset uint-buf 3 d)
     (aget float-buf 0)))

Complete namespace definition

(ns thi.ng.glsl.buffers
  #?(:clj
     (:import
      [java.nio ByteBuffer FloatBuffer]))
  (:require
   [thi.ng.glsl.core :as glsl :include-macros true]))

(glsl/defglsl pack-float
  nil "
<<pack-float>>")

<<unpack-float>>