/** Random number generator
*/
-static unsigned int seed_x = 521288629;
-static unsigned int seed_y = 362436069;
+typedef struct
+{
+ unsigned int x;
+ unsigned int y;
+} rand_seed;
+
+static void init_seed( rand_seed* seed, int init )
+{
+ // Use the initial value to initialize the seed to arbitrary values.
+ // This causes the algorithm to produce consistent results each time for the same frame number.
+ seed->x = 521288629 + init - ( init << 16 );
+ seed->y = 362436069 - init + ( init << 16 );
+}
-static inline unsigned int fast_rand( )
+static inline unsigned int fast_rand( rand_seed* seed )
{
- static unsigned int a = 18000, b = 30903;
- seed_x = a * ( seed_x & 65535 ) + ( seed_x >> 16 );
- seed_y = b * ( seed_y & 65535 ) + ( seed_y >> 16 );
- return ( ( seed_x << 16 ) + ( seed_y & 65535 ) );
+ static unsigned int a = 18000, b = 30903;
+ seed->x = a * ( seed->x & 65535 ) + ( seed->x >> 16 );
+ seed->y = b * ( seed->y & 65535 ) + ( seed->y >> 16 );
+ return ( ( seed->x << 16 ) + ( seed->y & 65535 ) );
}
// Foward declarations
// Value to hold a random number
uint32_t value;
+ // Initialize seed from the frame number.
+ rand_seed seed;
+ init_seed( &seed, mlt_frame_get_position( frame ) );
+
// Generate random noise
while ( p != *buffer )
{
- value = fast_rand( ) & 0xff;
+ value = fast_rand( &seed ) & 0xff;
*( -- p ) = 128;
*( -- p ) = value < 16 ? 16 : value > 240 ? 240 : value;
}
if ( *buffer != NULL )
{
int16_t *p = *buffer + size / 2;
- while ( p != *buffer )
- *( -- p ) = fast_rand( ) & 0x0f00;
+ rand_seed seed;
+ init_seed( &seed, mlt_frame_get_position( frame ) );
+ while ( p != *buffer )
+ *( -- p ) = fast_rand( &seed ) & 0x0f00;
}
// Set the buffer for destruction