SkBitmap_scroll.cpp revision 0910916c0f7b951ee55c4b7c6358295b9bca0565 
1#include "SkBitmap.h"
2#include "SkRegion.h"
3
4bool SkBitmap::scrollRect(const SkIRect* subset, int dx, int dy,
5                          SkRegion* inval) const
6{
7    if (NULL != subset) {
8        SkBitmap tmp;
9
10        return  this->extractSubset(&tmp, *subset) &&
11                // now call again with no rectangle
12                tmp.scrollRect(NULL, dx, dy, inval);
13    }
14
15    int shift;
16
17    switch (this->config()) {
18    case kIndex8_Config:
19    case kA8_Config:
20        shift = 0;
21        break;
22    case kARGB_4444_Config:
23    case kRGB_565_Config:
24        shift = 1;
25        break;
26    case kARGB_8888_Config:
27        shift = 2;
28        break;
29    default:
30        // can't scroll this config
31        return false;
32    }
33
34    int width = this->width();
35    int height = this->height();
36
37    // check if there's nothing to do
38    if ((dx | dy) == 0 || width <= 0 || height <= 0) {
39        if (NULL != inval) {
40            inval->setEmpty();
41        }
42        return true;
43    }
44
45    // compute the inval region now, before we see if there are any pixels
46    if (NULL != inval) {
47        SkIRect r;
48
49        r.set(0, 0, width, height);
50        // initial the region with the entire bounds
51        inval->setRect(r);
52        // do the "scroll"
53        r.offset(dx, dy);
54
55        // check if we scrolled completely away
56        if (!SkIRect::Intersects(r, inval->getBounds())) {
57            // inval has already been updated...
58            return true;
59        }
60
61        // compute the dirty area
62        inval->op(r, SkRegion::kDifference_Op);
63    }
64
65    SkAutoLockPixels    alp(*this);
66    // if we have no pixels, just return (inval is already updated)
67    // don't call readyToDraw(), since we don't require a colortable per se
68    if (this->getPixels() == NULL) {
69        return true;
70    }
71
72    // if we get this far, then we need to shift the pixels
73
74    char*       dst = (char*)this->getPixels();
75    const char* src = dst;
76    int         rowBytes = this->rowBytes();    // need rowBytes to be signed
77
78    if (dy <= 0) {
79        src -= dy * rowBytes;
80        height += dy;
81    } else {
82        dst += dy * rowBytes;
83        height -= dy;
84        // now jump src/dst to the last scanline
85        src += (height - 1) * rowBytes;
86        dst += (height - 1) * rowBytes;
87        // now invert rowbytes so we copy backwards in the loop
88        rowBytes = -rowBytes;
89    }
90
91    if (dx <= 0) {
92        src -= dx << shift;
93        width += dx;
94    } else {
95        dst += dx << shift;
96        width -= dx;
97    }
98
99    width <<= shift;    // now width is the number of bytes to move per line
100    while (--height >= 0) {
101        memmove(dst, src, width);
102        dst += rowBytes;
103        src += rowBytes;
104    }
105    return true;
106}
107
108