Fix pause for noise producer.

Sees the random number generator with the frame number so that subsequent "get_image" calls to the same frame produce the same image.

diff --git a/src/modules/core/producer_noise.c b/src/modules/core/producer_noise.c
index 0e39eb7a3097e2d4d78f190f7665b3bc0b3c6993..b894f51a3b098c3c0f90f2ba5948b7b30462c424 100644 (file)
--- a/src/modules/core/producer_noise.c
+++ b/src/modules/core/producer_noise.c
@@ -29,15 +29,26 @@
 /** 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
@@ -92,10 +103,14 @@ static int producer_get_image( mlt_frame frame, uint8_t **buffer, mlt_image_form
                // 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;
                }
@@ -124,8 +139,10 @@ static int producer_get_audio( mlt_frame frame, int16_t **buffer, mlt_audio_form
        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