ljpegdec: Support MCU in ljpeg_decode_yuv_scan()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mjpegdec.c

@@ -765,6 +765,8 @@ static int ljpeg_decode_yuv_scan(MJpegDecodeContext *s, int predictor, int point
     int i, mb_x, mb_y;
     const int nb_components=s->nb_components;
     int bits= (s->bits+7)&~7;
+    int resync_mb_y = 0;
+    int resync_mb_x = 0;
 
     point_transform += bits - s->bits;
 
@@ -772,10 +774,15 @@ static int ljpeg_decode_yuv_scan(MJpegDecodeContext *s, int predictor, int point
 
     for(mb_y = 0; mb_y < s->mb_height; mb_y++) {
         for(mb_x = 0; mb_x < s->mb_width; mb_x++) {
-            if (s->restart_interval && !s->restart_count)
+            if (s->restart_interval && !s->restart_count){
                 s->restart_count = s->restart_interval;
+                resync_mb_x = mb_x;
+                resync_mb_y = mb_y;
+            }
 
-            if(mb_x==0 || mb_y==0 || s->interlaced){
+            if(!mb_x || mb_y == resync_mb_y || mb_y == resync_mb_y+1 && mb_x < resync_mb_x || s->interlaced){
+                int toprow  = mb_y == resync_mb_y || mb_y == resync_mb_y+1 && mb_x < resync_mb_x;
+                int leftcol = !mb_x || mb_y == resync_mb_y && mb_x == resync_mb_x;
                 for(i=0;i<nb_components;i++) {
                     uint8_t *ptr;
                     uint16_t *ptr16;
@@ -798,14 +805,14 @@ static int ljpeg_decode_yuv_scan(MJpegDecodeContext *s, int predictor, int point
                             return -1;
                         if(bits<=8){
                         ptr = s->picture.data[c] + (linesize * (v * mb_y + y)) + (h * mb_x + x); //FIXME optimize this crap
-                        if(y==0 && mb_y==0){
-                            if(x==0 && mb_x==0){
+                        if(y==0 && toprow){
+                            if(x==0 && leftcol){
                                 pred= 1 << (bits - 1);
                             }else{
                                 pred= ptr[-1];
                             }
                         }else{
-                            if(x==0 && mb_x==0){
+                            if(x==0 && leftcol){
                                 pred= ptr[-linesize];
                             }else{
                                 PREDICT(pred, ptr[-linesize-1], ptr[-linesize], ptr[-1], predictor);
@@ -818,14 +825,14 @@ static int ljpeg_decode_yuv_scan(MJpegDecodeContext *s, int predictor, int point
                         *ptr= pred + (dc << point_transform);
                         }else{
                             ptr16 = s->picture.data[c] + 2*(linesize * (v * mb_y + y)) + 2*(h * mb_x + x); //FIXME optimize this crap
-                            if(y==0 && mb_y==0){
-                                if(x==0 && mb_x==0){
+                            if(y==0 && toprow){
+                                if(x==0 && leftcol){
                                     pred= 1 << (bits - 1);
                                 }else{
                                     pred= ptr16[-1];
                                 }
                             }else{
-                                if(x==0 && mb_x==0){
+                                if(x==0 && leftcol){
                                     pred= ptr16[-linesize];
                                 }else{
                                     PREDICT(pred, ptr16[-linesize-1], ptr16[-linesize], ptr16[-1], predictor);