Bmp Image Decoding

src/codec/SkMaskSwizzler.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkColorPriv.h"
+#include "SkMaskSwizzler.h"
+
+/*
+ *
+ * Row procedure for masked color components with 16 bits per pixel
+ *
+ */
+static SkSwizzler::ResultAlpha swizzle_mask16_to_n32(
+        void* dstRow, const uint8_t* srcRow, int width, SkMasks* masks) {
+
+    // Use the masks to decode to the destination
+    uint16_t* srcPtr = (uint16_t*) srcRow;
+    SkPMColor* dstPtr = (SkPMColor*) dstRow;
+    for (int i = 0; i < width; i++) {
+        uint16_t p = srcPtr[i];
+        uint8_t red = masks->getRed(p);
+        uint8_t green = masks->getGreen(p);
+        uint8_t blue = masks->getBlue(p);
+        dstPtr[i] = SkPackARGB32NoCheck(0xFF, red, green, blue);
+    }
+    return SkSwizzler::kOpaque_ResultAlpha;
+}
+
+/*
+ *
+ * Row procedure for masked color components with 16 bits per pixel with alpha
+ *
+ */
+static SkSwizzler::ResultAlpha swizzle_mask16_alpha_to_n32(
+        void* dstRow, const uint8_t* srcRow, int width, SkMasks* masks) {
+
+    // Use the masks to decode to the destination
+    uint16_t* srcPtr = (uint16_t*) srcRow;
+    SkPMColor* dstPtr = (SkPMColor*) dstRow;
+    uint8_t zeroAlpha = 0;
+    uint8_t maxAlpha = 0xFF;
+    for (int i = 0; i < width; i++) {
+        uint16_t p = srcPtr[i];
+        uint8_t red = masks->getRed(p);
+        uint8_t green = masks->getGreen(p);
+        uint8_t blue = masks->getBlue(p);
+        uint8_t alpha = masks->getAlpha(p);
+        zeroAlpha |= alpha;
+        maxAlpha &= alpha;
+        dstPtr[i] = SkPackARGB32NoCheck(alpha, red, green, blue);

[scroggo, 2015/03/11 21:14:26]

I think this is wrong. Is the intention to premultiply or not? If not,  maybe
make the name specify that it does not? (Is there a different version for
premultiplied?)

+    }
+    return SkSwizzler::GetResult(zeroAlpha, maxAlpha);
+}
+
+/*
+ *
+ * Row procedure for masked color components with 24 bits per pixel
+ *
+ */
+static SkSwizzler::ResultAlpha swizzle_mask24_to_n32(
+        void* dstRow, const uint8_t* srcRow, int width, SkMasks* masks) {
+
+    // Use the masks to decode to the destination
+    SkPMColor* dstPtr = (SkPMColor*) dstRow;
+    for (int i = 0; i < 3*width; i += 3) {
+        uint32_t p = srcRow[i] | (srcRow[i + 1] << 8) | srcRow[i + 2] << 16;
+        uint8_t red = masks->getRed(p);
+        uint8_t green = masks->getGreen(p);
+        uint8_t blue = masks->getBlue(p);
+        dstPtr[i/3] = SkPackARGB32NoCheck(0xFF, red, green, blue);
+    }
+    return SkSwizzler::kOpaque_ResultAlpha;
+}
+
+/*
+ *
+ * Row procedure for masked color components with 24 bits per pixel with alpha
+ *
+ */
+static SkSwizzler::ResultAlpha swizzle_mask24_alpha_to_n32(
+        void* dstRow, const uint8_t* srcRow, int width, SkMasks* masks) {
+
+    // Use the masks to decode to the destination
+    SkPMColor* dstPtr = (SkPMColor*) dstRow;
+    uint8_t zeroAlpha = 0;
+    uint8_t maxAlpha = 0xFF;
+    for (int i = 0; i < 3*width; i += 3) {
+        uint32_t p = srcRow[i] | (srcRow[i + 1] << 8) | srcRow[i + 2] << 16;
+        uint8_t red = masks->getRed(p);
+        uint8_t green = masks->getGreen(p);
+        uint8_t blue = masks->getBlue(p);
+        uint8_t alpha = masks->getAlpha(p);
+        zeroAlpha |= alpha;
+        maxAlpha &= alpha;
+        dstPtr[i/3] = SkPackARGB32NoCheck(alpha, red, green, blue);

[scroggo, 2015/03/11 21:14:26]

Again, this is only valid for unpremultiplied. (or opaque, if alpha is FF)

+    }
+    return SkSwizzler::GetResult(zeroAlpha, maxAlpha);
+}
+
+/*
+ *
+ * Row procedure for masked color components with 32 bits per pixel
+ *
+ */
+static SkSwizzler::ResultAlpha swizzle_mask32_to_n32(
+        void* dstRow, const uint8_t* srcRow, int width, SkMasks* masks) {
+
+    // Use the masks to decode to the destination
+    uint32_t* srcPtr = (uint32_t*) srcRow;
+    SkPMColor* dstPtr = (SkPMColor*) dstRow;
+    for (int i = 0; i < width; i++) {
+        uint32_t p = srcPtr[i];
+        uint8_t red = masks->getRed(p);
+        uint8_t green = masks->getGreen(p);
+        uint8_t blue = masks->getBlue(p);
+        dstPtr[i] = SkPackARGB32NoCheck(0xFF, red, green, blue);
+    }
+    return SkSwizzler::kOpaque_ResultAlpha;
+}
+
+/*
+ *
+ * Row procedure for masked color components with 32 bits per pixel
+ *
+ */
+static SkSwizzler::ResultAlpha swizzle_mask32_alpha_to_n32(
+        void* dstRow, const uint8_t* srcRow, int width, SkMasks* masks) {
+
+    // Use the masks to decode to the destination
+    uint32_t* srcPtr = (uint32_t*) srcRow;
+    SkPMColor* dstPtr = (SkPMColor*) dstRow;
+    uint8_t zeroAlpha = 0;
+    uint8_t maxAlpha = 0xFF;
+    for (int i = 0; i < width; i++) {
+        uint32_t p = srcPtr[i];
+        uint8_t red = masks->getRed(p);
+        uint8_t green = masks->getGreen(p);
+        uint8_t blue = masks->getBlue(p);
+        uint8_t alpha = masks->getAlpha(p);
+        zeroAlpha |= alpha;
+        maxAlpha &= alpha;
+        dstPtr[i] = SkPackARGB32NoCheck(alpha, red, green, blue);
+    }
+    return SkSwizzler::GetResult(zeroAlpha, maxAlpha);
+}
+
+/*
+ *
+ * Create a new mask swizzler
+ *
+ */
+SkMaskSwizzler* SkMaskSwizzler::CreateMaskSwizzler(
+        const SkImageInfo& imageInfo, SkMasks* masks, uint32_t bitsPerPixel) {
+
+    // Choose the appropriate row procedure
+    RowProc proc = NULL;
+    uint32_t alphaMask = masks->getAlphaMask();
+    switch (bitsPerPixel) {
+        case 16:
+            if (0 == alphaMask) {
+                proc = &swizzle_mask16_to_n32;
+            } else {
+                proc = &swizzle_mask16_alpha_to_n32;
+            }
+            break;
+        case 24:
+            if (0 == alphaMask) {
+                proc = &swizzle_mask24_to_n32;
+            } else {
+                proc = &swizzle_mask24_alpha_to_n32;
+            }
+            break;
+        case 32:
+            if (0 == alphaMask) {
+                proc = &swizzle_mask32_to_n32;
+            } else {
+                proc = &swizzle_mask32_alpha_to_n32;
+            }
+            break;
+        default:
+            SkASSERT(false);
+            return NULL;
+    }
+    return SkNEW_ARGS(SkMaskSwizzler, (imageInfo, masks, proc));
+}
+
+/*
+ *
+ * Constructor for mask swizzler
+ *
+ */
+SkMaskSwizzler::SkMaskSwizzler(const SkImageInfo& imageInfo,
+                               SkMasks* masks, RowProc proc)
+    : fImageInfo(imageInfo)
+    , fMasks(masks)
+    , fRowProc(proc)
+{}
+
+/*
+ *
+ * Swizzle the next row
+ *
+ */
+SkSwizzler::ResultAlpha SkMaskSwizzler::next(void* dst,
+                                             const uint8_t* src) {
+    return fRowProc(dst, src, fImageInfo.width(), fMasks);
+}