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"
+
+/*
+ *
+ * Used to convert 1-7 bit color components into 8-bit color components
+ *
+ */
+const static uint8_t n_bit_to_8_bit_lookup_table[] = {
+    // 1 bit
+    0, 255,
+    // 2 bits
+    0, 85, 170, 255,
+    // 3 bits
+    0, 36, 73, 109, 146, 182, 219, 255,
+    // 4 bits
+    0, 17, 34, 51, 68, 85, 102, 119, 136, 153, 170, 187, 204, 221, 238, 255,
+    // 5 bits
+    0, 8, 16, 25, 33, 41, 49, 58, 66, 74, 82, 90, 99, 107, 115, 123, 132, 140,
+    148, 156, 165, 173, 181, 189, 197, 206, 214, 222, 230, 239, 247, 255,
+    // 6 bits
+    0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 45, 49, 53, 57, 61, 65, 69, 73,
+    77, 81, 85, 89, 93, 97, 101, 105, 109, 113, 117, 121, 125, 130, 134, 138,
+    142, 146, 150, 154, 158, 162, 166, 170, 174, 178, 182, 186, 190, 194, 198,
+    202, 206, 210, 215, 219, 223, 227, 231, 235, 239, 243, 247, 251, 255,
+    // 7 bits
+    0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38,
+    40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76,
+    78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110,
+    112, 114, 116, 118, 120, 122, 124, 126, 129, 131, 133, 135, 137, 139, 141,
+    143, 145, 147, 149, 151, 153, 155, 157, 159, 161, 163, 165, 167, 169, 171,
+    173, 175, 177, 179, 181, 183, 185, 187, 189, 191, 193, 195, 197, 199, 201,
+    203, 205, 207, 209, 211, 213, 215, 217, 219, 221, 223, 225, 227, 229, 231,
+    233, 235, 237, 239, 241, 243, 245, 247, 249, 251, 253, 255
+};
+
+/*
+ *
+ * Convert an n bit component to an 8-bit component
+ *
+ */
+static uint8_t convert_to_8(uint32_t component, uint32_t n) {
+    if (0 == n) {
+        return 0;
+    } else if (8 > n) {
+        return n_bit_to_8_bit_lookup_table[(1 << n) - 2 + component];
+    } else {
+        SkASSERT(8 == n);
+        return component;
+    }
+}
+
+/*
+ *
+ * Get the color component
+ *
+ */
+static uint8_t get_comp(uint32_t pixel, uint32_t mask, uint32_t shift,
+                        uint32_t size) {
+    return convert_to_8((pixel & mask) >> shift, size);
+}
+
+/*
+ *
+ * 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,
+        const SkMaskSwizzler::Masks& masks) {
+
+    // Use the masks to decode to the destination
+    uint16_t* srcPtr = (uint16_t*) srcRow;
+    SkPMColor* dstPtr = (SkPMColor*) dstRow;
+    for (uint32_t i = 0; i < width; i++) {
+        uint16_t p = srcPtr[i];
+        uint8_t red = get_comp(p, masks.red.mask, masks.red.shift,

[scroggo, 2015/03/11 14:23:10]

get_comp is a step in the right direction.

What if Masks had some member functions:

Masks {
  ...
  uint8_t getRed(uint16_t p) {
    return getComp(red.mask, red.shift, red.size);
  }
private:
  static uint8_t getComp(...);
}

[msarett, 2015/03/11 18:53:05]

Agreed this is done.

+                               masks.red.size);
+        uint8_t green = get_comp(p, masks.green.mask, masks.green.shift,
+                                 masks.green.size);
+        uint8_t blue = get_comp(p, masks.blue.mask, masks.blue.shift,
+                                masks.blue.size);
+        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,
+        const SkMaskSwizzler::Masks& 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 (uint32_t i = 0; i < width; i++) {
+        uint16_t p = srcPtr[i];
+        uint8_t red = get_comp(p, masks.red.mask, masks.red.shift,
+                               masks.red.size);
+        uint8_t green = get_comp(p, masks.green.mask, masks.green.shift,
+                                 masks.green.size);
+        uint8_t blue = get_comp(p, masks.blue.mask, masks.blue.shift,
+                                masks.blue.size);
+        uint8_t alpha = get_comp(p, masks.alpha.mask, masks.alpha.shift,
+                                 masks.alpha.size);
+        zeroAlpha |= alpha;
+        maxAlpha &= alpha;
+        dstPtr[i] = SkPackARGB32NoCheck(alpha, red, green, blue);
+    }
+    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,
+        const SkMaskSwizzler::Masks& masks) {
+
+    // Use the masks to decode to the destination
+    SkPMColor* dstPtr = (SkPMColor*) dstRow;
+    for (uint32_t i = 0; i < 3*width; i += 3) {
+        uint32_t p = srcRow[i] | (srcRow[i + 1] << 8) | srcRow[i + 2] << 16;
+        uint8_t red = get_comp(p, masks.red.mask, masks.red.shift,
+                               masks.red.size);
+        uint8_t green = get_comp(p, masks.green.mask, masks.green.shift,
+                                 masks.green.size);
+        uint8_t blue = get_comp(p, masks.blue.mask, masks.blue.shift,
+                                masks.blue.size);
+        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,
+        const SkMaskSwizzler::Masks& masks) {
+
+    // Use the masks to decode to the destination
+    SkPMColor* dstPtr = (SkPMColor*) dstRow;
+    uint8_t zeroAlpha = 0;
+    uint8_t maxAlpha = 0xFF;
+    for (uint32_t i = 0; i < 3*width; i += 3) {
+        uint32_t p = srcRow[i] | (srcRow[i + 1] << 8) | srcRow[i + 2] << 16;
+        uint8_t red = get_comp(p, masks.red.mask, masks.red.shift,
+                               masks.red.size);
+        uint8_t green = get_comp(p, masks.green.mask, masks.green.shift,
+                                 masks.green.size);
+        uint8_t blue = get_comp(p, masks.blue.mask, masks.blue.shift,
+                                masks.blue.size);
+        uint8_t alpha = get_comp(p, masks.alpha.mask, masks.alpha.shift,
+                                 masks.alpha.size);
+        zeroAlpha |= alpha;
+        maxAlpha &= alpha;
+        dstPtr[i/3] = SkPackARGB32NoCheck(alpha, red, green, blue);
+    }
+    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,
+        const SkMaskSwizzler::Masks& masks) {
+
+    // Use the masks to decode to the destination
+    uint32_t* srcPtr = (uint32_t*) srcRow;
+    SkPMColor* dstPtr = (SkPMColor*) dstRow;
+    for (uint32_t i = 0; i < width; i++) {
+        uint32_t p = srcPtr[i];
+        uint8_t red = get_comp(p, masks.red.mask, masks.red.shift,
+                               masks.red.size);
+        uint8_t green = get_comp(p, masks.green.mask, masks.green.shift,
+                                 masks.green.size);
+        uint8_t blue = get_comp(p, masks.blue.mask, masks.blue.shift,
+                                masks.blue.size);
+        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,
+        const SkMaskSwizzler::Masks& 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 (uint32_t i = 0; i < width; i++) {
+        uint32_t p = srcPtr[i];
+        uint8_t red = get_comp(p, masks.red.mask, masks.red.shift,
+                               masks.red.size);
+        uint8_t green = get_comp(p, masks.green.mask, masks.green.shift,
+                                 masks.green.size);
+        uint8_t blue = get_comp(p, masks.blue.mask, masks.blue.shift,
+                                masks.blue.size);
+        uint8_t alpha = get_comp(p, masks.alpha.mask, masks.alpha.shift,
+                                 masks.alpha.size);
+        zeroAlpha |= alpha;
+        maxAlpha &= alpha;
+        dstPtr[i] = SkPackARGB32NoCheck(alpha, red, green, blue);
+    }
+    return SkSwizzler::GetResult(zeroAlpha, maxAlpha);
+}
+
+/*
+ *
+ * Process an input mask to obtain the necessary information
+ *
+ */
+const SkMaskSwizzler::MaskInfo& SkMaskSwizzler::ProcessMask(uint32_t mask,
+                                                            uint32_t bpp) {
+    // Trim the masks to the allowed number of bits
+    if (bpp < 32) {
+        mask &= (1 << bpp) - 1;
+    }
+
+    // Determine properties of the mask
+    uint32_t tempMask = mask;
+    uint32_t shift = 0;
+    uint32_t size = 0;
+    if (tempMask != 0) {
+        // Count trailing zeros on masks
+        for (; (tempMask & 1) == 0; tempMask >>= 1) {
+            shift++;
+        }
+        // Count the size of the mask
+        for (; tempMask & 1; tempMask >>= 1) {
+            size++;
+        }
+        // Truncate masks greater than 8 bits
+        if (size > 8) {
+            shift += size - 8;
+            size = 8;
+        }
+    }
+
+    // Save the calculated values
+    const MaskInfo info = { mask, shift, size };
+    return info;
+}
+
+/*
+ *
+ * Create a new mask swizzler
+ *
+ */
+SkMaskSwizzler* SkMaskSwizzler::CreateMaskSwizzler(
+        const SkImageInfo& imageInfo, InputMasks input, uint32_t bitsPerPixel) {
+    // Process input masks
+    const MaskInfo red = ProcessMask(input.red, bitsPerPixel);
+    const MaskInfo green = ProcessMask(input.green, bitsPerPixel);
+    const MaskInfo blue = ProcessMask(input.blue, bitsPerPixel);
+    const MaskInfo alpha = ProcessMask(input.alpha, bitsPerPixel);
+    const Masks masks = { red, green, blue, alpha };
+
+    // Choose the appropriate row procedure
+    RowProc proc = NULL;
+    switch (bitsPerPixel) {
+        case 16:
+            if (masks.alpha.mask == 0) {
+                proc = &swizzle_mask16_to_n32;
+            } else {
+                proc = &swizzle_mask16_alpha_to_n32;
+            }
+            break;
+        case 24:
+            if (masks.alpha.mask == 0) {
+                proc = &swizzle_mask24_to_n32;
+            } else {
+                proc = &swizzle_mask24_alpha_to_n32;
+            }
+            break;
+        case 32:
+            if (masks.alpha.mask == 0) {
+                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, const Masks& 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);
+}