add readPixels() to SkBitmap

src/core/SkConfig8888.cpp

Index: src/core/SkConfig8888.cpp
diff --git a/src/core/SkConfig8888.cpp b/src/core/SkConfig8888.cpp
index 189309dae6e97b51c6d410a222f4880c2a831365..474db5b1244281c12d4bf356d424d6ab26c02d43 100644
--- a/src/core/SkConfig8888.cpp
+++ b/src/core/SkConfig8888.cpp
@@ -1,5 +1,8 @@
+#include "SkBitmap.h"

[scroggo, 2014/07/10 15:09:48]

Could you add the copyright header as well?

[reed1, 2014/07/10 15:32:16]

Done.

+#include "SkCanvas.h"
 #include "SkConfig8888.h"
 #include "SkColorPriv.h"
+#include "SkDither.h"
 #include "SkMathPriv.h"
 #include "SkUnPreMultiply.h"
 
@@ -115,3 +118,135 @@ bool SkSrcPixelInfo::convertPixelsTo(SkDstPixelInfo* dst, int width, int height)
     }
     return true;
 }
+
+static void rect_memcpy(void* dst, size_t dstRB, const void* src, size_t srcRB, size_t bytesPerRow,
+                        int rowCount) {
+    SkASSERT(bytesPerRow <= srcRB);
+    SkASSERT(bytesPerRow <= dstRB);
+    for (int i = 0; i < rowCount; ++i) {
+        memcpy(dst, src, bytesPerRow);
+        dst = (char*)dst + dstRB;
+        src = (const char*)src + srcRB;
+    }
+}
+
+bool SkPixelInfo::CopyPixels(const SkImageInfo& dstInfo, void* dstPixels, size_t dstRB,
+                             const SkImageInfo& srcInfo, const void* srcPixels, size_t srcRB,
+                             SkColorTable* ctable) {
+    if (srcInfo.dimensions() != dstInfo.dimensions()) {
+        return false;
+    }
+
+    const int width = srcInfo.width();
+    const int height = srcInfo.height();
+
+    // Handle fancy alpha swizzling if both are ARGB32
+    if (4 == srcInfo.bytesPerPixel() && 4 == dstInfo.bytesPerPixel()) {
+        SkDstPixelInfo dstPI;
+        dstPI.fColorType = dstInfo.colorType();
+        dstPI.fAlphaType = dstInfo.alphaType();
+        dstPI.fPixels = dstPixels;
+        dstPI.fRowBytes = dstRB;
+        
+        SkSrcPixelInfo srcPI;
+        srcPI.fColorType = srcInfo.colorType();
+        srcPI.fAlphaType = srcInfo.alphaType();
+        srcPI.fPixels = srcPixels;
+        srcPI.fRowBytes = srcRB;
+        
+        return srcPI.convertPixelsTo(&dstPI, width, height);
+    }
+
+    // If they agree on colorType, then we ignore alphaType and just memcpy.

[scroggo, 2014/07/10 15:09:48]

I'm not sure this is the correct behavior (it's also not true in the case of
4444). If we do behave this way, can you add a comment in the declaration?

[reed1, 2014/07/10 15:32:16]

This is what we did in the old code for both copyTo and readPixels. However, I
agree it might not be strictly correct.

I will update the above comment to reflect 4444's check, and/or handle this more
non-blindly.

+    // Note: we've already taken care of 32bit colortypes above.
+    if (srcInfo.colorType() == dstInfo.colorType()) {
+        switch (srcInfo.colorType()) {
+            case kRGB_565_SkColorType:
+            case kAlpha_8_SkColorType:
+            case kIndex_8_SkColorType:
+                break;
+            case kARGB_4444_SkColorType:
+                if (srcInfo.alphaType() != dstInfo.alphaType()) {
+                    return false;
+                }
+                break;
+            default:
+                return false;
+        }
+        rect_memcpy(dstPixels, dstRB, srcPixels, srcRB, width * srcInfo.bytesPerPixel(), height);
+        return true;
+    }
+
+    /*
+     *  Begin section where we try to change colorTypes along the way. Not all combinations
+     *  are supported.
+     */
+
+    // Can no longer draw directly into 4444, but we can manually wack it for a few combinations

[scroggo, 2014/07/10 15:09:48]

whack*

[reed1, 2014/07/10 15:32:16]

Done.

+    if (kARGB_4444_SkColorType == dstInfo.colorType() &&
+        (kN32_SkColorType == srcInfo.colorType() || kIndex_8_SkColorType == srcInfo.colorType())) {
+        if (srcInfo.alphaType() == kUnpremul_SkAlphaType) {
+            // Our method for converting to 4444 assumes premultiplied.
+            return false;
+        }
+        
+        const SkPMColor* table = NULL;
+        if (kIndex_8_SkColorType == srcInfo.colorType()) {
+            if (NULL == ctable) {
+                return false;
+            }
+            table = ctable->lockColors();
+        }
+
+        for (int y = 0; y < height; ++y) {
+            DITHER_4444_SCAN(y);
+            SkPMColor16* SK_RESTRICT dstRow = (SkPMColor16*)dstPixels;
+            if (table) {
+                const uint8_t* SK_RESTRICT srcRow = (const uint8_t*)srcPixels;
+                for (int x = 0; x < width; ++x) {
+                    dstRow[x] = SkDitherARGB32To4444(table[srcRow[x]], DITHER_VALUE(x));
+                }
+            } else {
+                const SkPMColor* SK_RESTRICT srcRow = (const SkPMColor*)srcPixels;
+                for (int x = 0; x < width; ++x) {
+                    dstRow[x] = SkDitherARGB32To4444(srcRow[x], DITHER_VALUE(x));
+                }
+            }
+            dstPixels = (char*)dstPixels + dstRB;
+            srcPixels = (const char*)srcPixels + srcRB;
+        }
+        
+        if (table) {
+            ctable->unlockColors();
+        }
+        return true;
+    }
+
+    if (dstInfo.alphaType() == kUnpremul_SkAlphaType) {
+        // We do not support drawing to unpremultiplied bitmaps.
+        return false;
+    }
+
+    // Final fall-back, draw with a canvas
+    //
+    // Always clear the dest in case one of the blitters accesses it
+    // TODO: switch the allocation of tmpDst to call sk_calloc_throw
+    {
+        SkBitmap bm;
+        if (!bm.installPixels(srcInfo, const_cast<void*>(srcPixels), srcRB, ctable, NULL, NULL)) {
+            return false;
+        }
+        SkAutoTUnref<SkCanvas> canvas(SkCanvas::NewRasterDirect(dstInfo, dstPixels, dstRB));
+        if (NULL == canvas.get()) {
+            return false;
+        }
+
+        SkPaint  paint;
+        paint.setDither(true);
+
+        canvas->clear(0);
+        canvas->drawBitmap(bm, 0, 0, &paint);
+        return true;
+    }
+}
+