Adding anisotropic mipmap levels to SkMipMap.

src/core/SkMipMap.cpp

Index: src/core/SkMipMap.cpp
diff --git a/src/core/SkMipMap.cpp b/src/core/SkMipMap.cpp
index 1b630a0466cede5d910049e262a298a130bdc0cc..6747c3ab6f7a7c64fc139082af7c3d7e30c5ea21 100644
--- a/src/core/SkMipMap.cpp
+++ b/src/core/SkMipMap.cpp
@@ -80,46 +80,76 @@ template <typename T> T add_121(const T& a, const T& b, const T& c) {
 //  In those (odd) cases, we use a triangle filter, with 1-pixel overlap between samplings,
 //  else for even cases, we just use a 2x box filter.
 //
-//  This produces 4 possible filters: 2x2 2x3 3x2 3x3 where WxH indicates the number of src pixels
-//  we need to sample in each dimension to produce 1 dst pixel.
+//  This produces 4 possible isotropic filters: 2x2 2x3 3x2 3x3 where WxH indicates the number of
+//  src pixels we need to sample in each dimension to produce 1 dst pixel.
 //
+//  OpenGL expects a full mipmap stack to contain anisotropic space as well.
+//  This means a 100x1 image would continue down to a 50x1 image, 25x1 image...
+//  Because of this, we need 4 more anisotropic filters: 1x2, 1x3, 2x1, 3x1.
 
-template <typename F> void downsample_2_2(void* dst, const void* src, size_t srcRB, int count) {
+template <typename F> void downsample_1_2(void* dst, const void* src, size_t srcRB, int count) {
     auto p0 = static_cast<const typename F::Type*>(src);
-    auto p1 = (const typename F::Type*)((const char*)p0 + srcRB);
     auto d = static_cast<typename F::Type*>(dst);
 
     for (int i = 0; i < count; ++i) {
         auto c00 = F::Expand(p0[0]);
         auto c01 = F::Expand(p0[1]);
-        auto c10 = F::Expand(p1[0]);
-        auto c11 = F::Expand(p1[1]);
 
-        auto c = c00 + c10 + c01 + c11;
-        d[i] = F::Compact(c >> 2);
+        auto c = c00 + c01;
+        d[i] = F::Compact(c >> 1);
         p0 += 2;
-        p1 += 2;
     }
+
 }
 
-template <typename F> void downsample_3_2(void* dst, const void* src, size_t srcRB, int count) {

[mtklein, 2016/03/01 13:40:49]

As far as I can tell, the old functions follow the convention of downsample_x_y,
where x is the number of pixels taken from a given row horizontally, and y the
number of rows averaged vertically.  E.g.

_2_2:  a b
       c d 

_2_3:  a b
       c d
       e f

_3_2:  a b c
       d e f

I think you have adopted the opposite convention for these new filters:

_1_3: a b c

_2_1: a
      b

This seems at best confusing, probably buggy?

[cblume, 2016/03/01 19:28:36]

You are right.
This should be fixed now (plus adding some extra SkASSERT(count > 0); calls).

+template <typename F> void downsample_1_3(void* dst, const void* src, size_t srcRB, int count) {
     SkASSERT(count > 0);
     auto p0 = static_cast<const typename F::Type*>(src);
-    auto p1 = (const typename F::Type*)((const char*)p0 + srcRB);
     auto d = static_cast<typename F::Type*>(dst);
 
     auto c02 = F::Expand(p0[0]);
-    auto c12 = F::Expand(p1[0]);
     for (int i = 0; i < count; ++i) {
         auto c00 = c02;
         auto c01 = F::Expand(p0[1]);
              c02 = F::Expand(p0[2]);
-        auto c10 = c12;
+
+        auto c = add_121(c00, c01, c02);
+        d[i] = F::Compact(c >> 2);
+        p0 += 2;
+    }
+
+}
+
+template <typename F> void downsample_2_1(void* dst, const void* src, size_t srcRB, int count) {
+    auto p0 = static_cast<const typename F::Type*>(src);
+    auto p1 = (const typename F::Type*)((const char*)p0 + srcRB);
+    auto d = static_cast<typename F::Type*>(dst);
+
+    for (int i = 0; i < count; ++i) {
+        auto c00 = F::Expand(p0[0]);
+        auto c10 = F::Expand(p1[0]);
+
+        auto c = c00 + c10;
+        d[i] = F::Compact(c >> 1);
+        p0 += 2;
+        p1 += 2;
+    }
+
+}
+
+template <typename F> void downsample_2_2(void* dst, const void* src, size_t srcRB, int count) {
+    auto p0 = static_cast<const typename F::Type*>(src);
+    auto p1 = (const typename F::Type*)((const char*)p0 + srcRB);
+    auto d = static_cast<typename F::Type*>(dst);
+
+    for (int i = 0; i < count; ++i) {
+        auto c00 = F::Expand(p0[0]);
+        auto c01 = F::Expand(p0[1]);
+        auto c10 = F::Expand(p1[0]);
         auto c11 = F::Expand(p1[1]);
-             c12 = F::Expand(p1[2]);
 
-        auto c = add_121(c00, c01, c02) + add_121(c10, c11, c12);
-        d[i] = F::Compact(c >> 3);
+        auto c = c00 + c10 + c01 + c11;
+        d[i] = F::Compact(c >> 2);
         p0 += 2;
         p1 += 2;
     }
@@ -147,6 +177,49 @@ template <typename F> void downsample_2_3(void* dst, const void* src, size_t src
     }
 }
 
+template <typename F> void downsample_3_1(void* dst, const void* src, size_t srcRB, int count) {
+    auto p0 = static_cast<const typename F::Type*>(src);
+    auto p1 = (const typename F::Type*)((const char*)p0 + srcRB);
+    auto p2 = (const typename F::Type*)((const char*)p1 + srcRB);
+    auto d = static_cast<typename F::Type*>(dst);
+
+    for (int i = 0; i < count; ++i) {
+        auto c00 = F::Expand(p0[0]);
+        auto c10 = F::Expand(p1[0]);
+        auto c20 = F::Expand(p2[0]);
+
+        auto c = add_121(c00, c10, c20);
+        d[i] = F::Compact(c >> 2);
+        p0 += 2;
+        p1 += 2;
+        p2 += 2;
+    }
+
+}
+
+template <typename F> void downsample_3_2(void* dst, const void* src, size_t srcRB, int count) {
+    SkASSERT(count > 0);
+    auto p0 = static_cast<const typename F::Type*>(src);
+    auto p1 = (const typename F::Type*)((const char*)p0 + srcRB);
+    auto d = static_cast<typename F::Type*>(dst);
+
+    auto c02 = F::Expand(p0[0]);
+    auto c12 = F::Expand(p1[0]);
+    for (int i = 0; i < count; ++i) {
+        auto c00 = c02;
+        auto c01 = F::Expand(p0[1]);
+             c02 = F::Expand(p0[2]);
+        auto c10 = c12;
+        auto c11 = F::Expand(p1[1]);
+             c12 = F::Expand(p1[2]);
+
+        auto c = add_121(c00, c01, c02) + add_121(c10, c11, c12);
+        d[i] = F::Compact(c >> 3);
+        p0 += 2;
+        p1 += 2;
+    }
+}
+
 template <typename F> void downsample_3_3(void* dst, const void* src, size_t srcRB, int count) {
     auto p0 = static_cast<const typename F::Type*>(src);
     auto p1 = (const typename F::Type*)((const char*)p0 + srcRB);
@@ -191,8 +264,12 @@ size_t SkMipMap::AllocLevelsSize(int levelCount, size_t pixelSize) {
 SkMipMap* SkMipMap::Build(const SkPixmap& src, SkDiscardableFactoryProc fact) {
     typedef void FilterProc(void*, const void* srcPtr, size_t srcRB, int count);
 
+    FilterProc* proc_1_2 = nullptr;
+    FilterProc* proc_1_3 = nullptr;
+    FilterProc* proc_2_1 = nullptr;
     FilterProc* proc_2_2 = nullptr;
     FilterProc* proc_2_3 = nullptr;
+    FilterProc* proc_3_1 = nullptr;
     FilterProc* proc_3_2 = nullptr;
     FilterProc* proc_3_3 = nullptr;
 
@@ -201,27 +278,43 @@ SkMipMap* SkMipMap::Build(const SkPixmap& src, SkDiscardableFactoryProc fact) {
     switch (ct) {
         case kRGBA_8888_SkColorType:
         case kBGRA_8888_SkColorType:
+            proc_1_2 = downsample_1_2<ColorTypeFilter_8888>;
+            proc_1_3 = downsample_1_3<ColorTypeFilter_8888>;
+            proc_2_1 = downsample_2_1<ColorTypeFilter_8888>;
             proc_2_2 = downsample_2_2<ColorTypeFilter_8888>;
             proc_2_3 = downsample_2_3<ColorTypeFilter_8888>;
+            proc_3_1 = downsample_3_1<ColorTypeFilter_8888>;
             proc_3_2 = downsample_3_2<ColorTypeFilter_8888>;
             proc_3_3 = downsample_3_3<ColorTypeFilter_8888>;
             break;
         case kRGB_565_SkColorType:
+            proc_1_2 = downsample_1_2<ColorTypeFilter_565>;
+            proc_1_3 = downsample_1_3<ColorTypeFilter_565>;
+            proc_2_1 = downsample_2_1<ColorTypeFilter_565>;
             proc_2_2 = downsample_2_2<ColorTypeFilter_565>;
             proc_2_3 = downsample_2_3<ColorTypeFilter_565>;
+            proc_3_1 = downsample_3_1<ColorTypeFilter_565>;
             proc_3_2 = downsample_3_2<ColorTypeFilter_565>;
             proc_3_3 = downsample_3_3<ColorTypeFilter_565>;
             break;
         case kARGB_4444_SkColorType:
+            proc_1_2 = downsample_1_2<ColorTypeFilter_4444>;
+            proc_1_3 = downsample_1_3<ColorTypeFilter_4444>;
+            proc_2_1 = downsample_2_1<ColorTypeFilter_4444>;
             proc_2_2 = downsample_2_2<ColorTypeFilter_4444>;
             proc_2_3 = downsample_2_3<ColorTypeFilter_4444>;
+            proc_3_1 = downsample_3_1<ColorTypeFilter_4444>;
             proc_3_2 = downsample_3_2<ColorTypeFilter_4444>;
             proc_3_3 = downsample_3_3<ColorTypeFilter_4444>;
             break;
         case kAlpha_8_SkColorType:
         case kGray_8_SkColorType:
+            proc_1_2 = downsample_1_2<ColorTypeFilter_8>;
+            proc_1_3 = downsample_1_3<ColorTypeFilter_8>;
+            proc_2_1 = downsample_2_1<ColorTypeFilter_8>;
             proc_2_2 = downsample_2_2<ColorTypeFilter_8>;
             proc_2_3 = downsample_2_3<ColorTypeFilter_8>;
+            proc_3_1 = downsample_3_1<ColorTypeFilter_8>;
             proc_3_2 = downsample_3_2<ColorTypeFilter_8>;
             proc_3_3 = downsample_3_3<ColorTypeFilter_8>;
             break;
@@ -231,6 +324,9 @@ SkMipMap* SkMipMap::Build(const SkPixmap& src, SkDiscardableFactoryProc fact) {
             return nullptr;
     }
 
+    if (src.width() <= 1 && src.height() <= 1) {
+        return nullptr;
+    }
     // whip through our loop to compute the exact size needed
     size_t  size = 0;
     int countLevels = 0;
@@ -239,17 +335,16 @@ SkMipMap* SkMipMap::Build(const SkPixmap& src, SkDiscardableFactoryProc fact) {
         int height = src.height();
         for (;;) {
             width >>= 1;
+            width = SkTMax(1, width);
             height >>= 1;
-            if (0 == width || 0 == height) {
-                break;
-            }
+            height = SkTMax(1, height);
             size += SkColorTypeMinRowBytes(ct, width) * height;
             countLevels += 1;
+            if (1 == width && 1 == height) {
+                break;
+            }
         }
     }
-    if (0 == countLevels) {
-        return nullptr;
-    }
 
     SkASSERT(countLevels == SkMipMap::ComputeLevelCount(src.width(), src.height()));
 
@@ -283,21 +378,39 @@ SkMipMap* SkMipMap::Build(const SkPixmap& src, SkDiscardableFactoryProc fact) {
 
     for (int i = 0; i < countLevels; ++i) {
         FilterProc* proc;
-        if (height & 1) {        // src-height is 3
-            if (width & 1) {    // src-width is 3
-                proc = proc_3_3;
-            } else {            // src-width is 2
-                proc = proc_2_3;
+        if (height & 1) {
+            if (height == 1) {        // src-height is 1
+                if (width & 1) {      // src-width is 3
+                    proc = proc_3_1;
+                } else {              // src-width is 2
+                    proc = proc_2_1;
+                }
+            } else {                  // src-height is 3
+                if (width & 1) {
+                    if (width == 1) { // src-width is 1
+                        proc = proc_1_3;
+                    } else {          // src-width is 3
+                        proc = proc_3_3;
+                    }
+                } else {              // src-width is 2
+                    proc = proc_2_3;
+                }
             }
-        } else {                // src-height is 2
-            if (width & 1) {    // src-width is 3
-                proc = proc_3_2;
-            } else {            // src-width is 2
+        } else {                      // src-height is 2
+            if (width & 1) {
+                if (width == 1) {     // src-width is 1
+                    proc = proc_1_2;
+                } else {              // src-width is 3
+                    proc = proc_3_2;
+                }
+            } else {                  // src-width is 2
                 proc = proc_2_2;
             }
         }
         width >>= 1;
+        width = SkTMax(1, width);
         height >>= 1;
+        height = SkTMax(1, height);
         rowBytes = SkToU32(SkColorTypeMinRowBytes(ct, width));
 
         levels[i].fPixmap = SkPixmap(SkImageInfo::Make(width, height, ct, at), addr, rowBytes);
@@ -323,27 +436,21 @@ SkMipMap* SkMipMap::Build(const SkPixmap& src, SkDiscardableFactoryProc fact) {
 }
 
 int SkMipMap::ComputeLevelCount(int baseWidth, int baseHeight) {
+    if (baseWidth < 1 || baseHeight < 1) {
+        return 0;
+    }
+
     // OpenGL's spec requires that each mipmap level have height/width equal to
     // max(1, floor(original_height / 2^i)
     // (or original_width) where i is the mipmap level.
     // Continue scaling down until both axes are size 1.
-    //
-    // This means it maintains isotropic space (both axes scaling down
-    // at the same rate) until one axis hits size 1.
-    // At that point, OpenGL continues to scale down into anisotropic space
-    // (where the scales are not the same between axes).
-    //
-    // Skia currently does not go into anisotropic space.
-    // Once an axis hits size 1 we stop.
-    // All this means is rather than use the largest axis we will use the
-    // smallest axis.
-
-    const int smallestAxis = SkTMin(baseWidth, baseHeight);
-    if (smallestAxis < 2) {
+
+    const int largestAxis = SkTMax(baseWidth, baseHeight);
+    if (largestAxis < 2) {
         // SkMipMap::Build requires a minimum size of 2.
         return 0;
     }
-    const int leadingZeros = SkCLZ(static_cast<uint32_t>(smallestAxis));
+    const int leadingZeros = SkCLZ(static_cast<uint32_t>(largestAxis));
     // If the value 00011010 has 3 leading 0s then it has 5 significant bits
     // (the bits which are not leading zeros)
     const int significantBits = (sizeof(uint32_t) * 8) - leadingZeros;