Anyone know what the story is with BlackWhiteFilter.java?
As far as I can tell, it has nothing to do with making stuff black and
white. The output is in full color.
Here's the brains behind it:
private final String mBlackWhiteShader =
"precision mediump float;\n" +
"uniform sampler2D tex_sampler_0;\n" +
"uniform vec2 seed;\n" +
"uniform float black;\n" +
"uniform float scale;\n" +
"uniform float stepsize;\n" +
"varying vec2 v_texcoord;\n" +
"float rand(vec2 loc) {\n" +
// Compute sin(theta), theta = 12.9898 x + 78.233y
// because floating point has limited range, make theta =
theta1 + theta2
// where theta1 = 12x + 78y and theta2 = 0.9898x + 0.233y)
// Note that theta1 and theta2 cover diffent range of theta.
" float theta1 = dot(loc, vec2(0.9898, 0.233));\n" +
" float theta2 = dot(loc, vec2(12.0, 78.0));\n" +
// Use the property sin(theta) =
cos(theta1)*sin(theta2)+sin(theta1)*cos(theta2)
// this approach also increases the precisions of sin(theta)
" float value = cos(theta1) * sin(theta2) + sin(theta1) *
cos(theta2);\n" +
// fract(43758.5453 * x) = fract(43758 * x + 0.5453 * x)
// keep value of part1 in range: (2^-14 to 2^14). Since 43758 =
117 * 374
// fract(43758 * sin(theta)) = mod(221 * mod(198*sin(theta),
1.0), 1.0)
// also to keep as much decimal digits, use the property
// mod(mod(198*sin(theta)) = mod(mod(197*sin(theta) +
sin(theta))
" float temp = mod(197.0 * value, 1.0) + value;\n" +
" float part1 = mod(220.0 * temp, 1.0) + temp;\n" +
" float part2 = value * 0.5453;\n" +
" float part3 = cos(theta1 + theta2) * 0.43758;\n" +
" return fract(part1 + part2 + part3);\n" +
"}\n" +
"void main() {\n" +
" vec4 color = texture2D(tex_sampler_0, v_texcoord);\n" +
" float dither = rand(v_texcoord + seed);\n" +
" vec3 xform = clamp((color.rgb - black) * scale, 0.0,
1.0);\n" +
" vec3 temp = clamp((color.rgb + stepsize - black) * scale,
0.0, 1.0);\n" +
" vec3 new_color = clamp(xform + (temp - xform) * (dither -
0.5), 0.0, 1.0);\n" +
" gl_FragColor = vec4(new_color, color.a);\n" +
"}\n";
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