Add memory decay color table creation program.

extra/color.cpp

@@ -0,0 +1,77 @@
+#include <algorithm>
+#include <string.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <math.h>
+
+inline float sqrtfast( float v )
+{
+    union
+    {
+        int i;
+        float f;
+    } u;
+
+    u.f = v;
+    u.i -= 1 << 23;
+    u.i >>= 1;
+    u.i += 1 << 29;
+    return u.f;
+}
+
+inline float linear2sRGB( float v )
+{
+    float s1 = sqrtfast( v );
+    float s2 = sqrtfast( s1 );
+    float s3 = sqrtfast( s2 );
+    return 0.585122381f * s1 + 0.783140355f * s2 - 0.368262736f * s3;
+}
+
+int lerp( int v0, int v1, float t )
+{
+    return int( ( 1-t ) * v0 + t * v1 );
+}
+
+inline float sRGB2linear( float v )
+{
+    return v * ( v * ( v * 0.305306011f + 0.682171111f ) + 0.012522878f );
+}
+
+int main()
+{
+    int c0 = std::min( 255, int( sRGB2linear( 1.f ) * 255 ) );
+    int c1 = std::min( 255, int( sRGB2linear( 0x44 / 255.f ) * 255 ) );
+
+    int s0 = std::min( 255, int( sRGB2linear( 1.f ) * 255 * 0.5 ) );
+    int s1 = std::min( 255, int( sRGB2linear( 0x44 / 255.f ) * 255 * 0.5 ) );
+
+    float target = 80.f;
+
+    uint32_t t[256];
+    memset( t, 0, sizeof( uint32_t ) * 256 );
+
+    for( int i=1; i<128; i++ )
+    {
+        float m = (i-1) / target;
+        int l0 = std::min( 255, lerp( s0, c0, m ) );
+        int l1 = std::min( 255, lerp( s1, c1, m ) );
+        int g0 = std::min( 255, int( linear2sRGB( l0/255.f ) * 255 ) );
+        int g1 = std::min( 255, int( linear2sRGB( l1/255.f ) * 255 ) );
+        g0 = l0;
+        g1 = l1;
+        t[i] = 0xFF000000 | ( g1 << 16 ) | ( g0 << 8 ) | g1;
+        t[uint8_t(-i)] = 0xFF000000 | ( g1 << 16 ) | ( g1 << 8 ) | g0;
+    }
+
+    printf( "uint32_t MemDecayColor[256] = {\n" );
+    for( int i=0; i<256; i += 8 )
+    {
+        printf( "   " );
+        for( int j=i; j<i+8; j++ )
+        {
+            printf( " 0x%X,", t[j] );
+        }
+        printf( "\n" );
+    }
+    printf( "};\n" );
+}