Adding direct access to SkMipMap levels.

tests/MipMapTest.cpp

Index: tests/MipMapTest.cpp
diff --git a/tests/MipMapTest.cpp b/tests/MipMapTest.cpp
index 32fa34f8fb7d226df8a8d08177f3544723fd44e5..027c04635306e0b399d9c3a08a6dd831fe4d13d1 100644
--- a/tests/MipMapTest.cpp
+++ b/tests/MipMapTest.cpp
@@ -10,12 +10,8 @@
 #include "SkRandom.h"
 #include "Test.h"
 
-static void make_bitmap(SkBitmap* bm, SkRandom& rand) {
-    // for now, Build needs a min size of 2, otherwise it will return nullptr.
-    // should fix that to support 1 X N, where N > 1 to return non-null.
-    int w = 2 + rand.nextU() % 1000;
-    int h = 2 + rand.nextU() % 1000;
-    bm->allocN32Pixels(w, h);
+static void make_bitmap(SkBitmap* bm, int width, int height) {
+    bm->allocN32Pixels(width, height);
     bm->eraseColor(SK_ColorWHITE);
 }
 
@@ -24,9 +20,14 @@ DEF_TEST(MipMap, reporter) {
     SkRandom rand;
 
     for (int i = 0; i < 500; ++i) {
-        make_bitmap(&bm, rand);
+        // for now, Build needs a min size of 2, otherwise it will return nullptr.
+        // should fix that to support 1 X N, where N > 1 to return non-null.
+        int width = 2 + rand.nextU() % 1000;
+        int height = 2 + rand.nextU() % 1000;
+        make_bitmap(&bm, width, height);
         SkAutoTUnref<SkMipMap> mm(SkMipMap::Build(bm, nullptr));
 
+        REPORTER_ASSERT(reporter, mm->countLevels() == SkMipMap::ComputeLevelCount(width, height));
         REPORTER_ASSERT(reporter, !mm->extractLevel(SkSize::Make(SK_Scalar1, SK_Scalar1),
                                                     nullptr));
         REPORTER_ASSERT(reporter, !mm->extractLevel(SkSize::Make(SK_Scalar1 * 2, SK_Scalar1 * 2),
@@ -55,3 +56,99 @@ DEF_TEST(MipMap, reporter) {
         }
     }
 }
+
+static void test_mipmap_generation(int width, int height, int expectedMipLevelCount,
+                                   skiatest::Reporter* reporter) {
+    SkBitmap bm;
+    bm.allocN32Pixels(width, height);
+    bm.eraseColor(SK_ColorWHITE);
+    SkAutoTUnref<SkMipMap> mm(SkMipMap::Build(bm, nullptr));
+
+    const int mipLevelCount = mm->countLevels();
+    REPORTER_ASSERT(reporter, mipLevelCount == expectedMipLevelCount);
+    for (int i = 0; i < mipLevelCount; ++i) {
+        SkMipMap::Level level;
+        REPORTER_ASSERT(reporter, mm->getLevel(i, &level));
+        // Make sure the mipmaps contain valid data and that the sizes are correct
+        REPORTER_ASSERT(reporter, level.fPixmap.addr());
+
+        // + 1 because SkMipMap does not include the base mipmap level.
+        int twoToTheMipLevel = 1 << (i + 1);
+        int currentWidth = width / twoToTheMipLevel;
+        int currentHeight = height / twoToTheMipLevel;
+        REPORTER_ASSERT(reporter, level.fPixmap.width() == currentWidth);
+        REPORTER_ASSERT(reporter, level.fPixmap.height() == currentHeight);
+    }
+}
+
+DEF_TEST(MipMap_DirectLevelAccess, reporter) {
+    // create mipmap with invalid size
+    {
+        // SkMipMap current requires the dimensions be greater than 2x2
+        SkBitmap bm;
+        bm.allocN32Pixels(1, 1);
+        bm.eraseColor(SK_ColorWHITE);
+        SkAutoTUnref<SkMipMap> mm(SkMipMap::Build(bm, nullptr));
+
+        REPORTER_ASSERT(reporter, mm == nullptr);
+    }
+
+    // check small mipmap's count and levels
+    // There should be 5 mipmap levels generated:
+    // 16x16, 8x8, 4x4, 2x2, 1x1
+    test_mipmap_generation(32, 32, 5, reporter);
+
+    // check large mipmap's count and levels
+    // There should be 9 mipmap levels generated:
+    // 500x500, 250x250, 125x125, 62x62, 31x31, 15x15, 7x7, 3x3, 1x1
+    test_mipmap_generation(1000, 1000, 9, reporter);
+}
+
+struct LevelCountScenario {
+    int fWidth;
+    int fHeight;
+    int fExpectedLevelCount;
+};
+
+DEF_TEST(MipMap_ComputeLevelCount, reporter) {
+    const LevelCountScenario tests[] = {
+        // Test mipmaps with negative sizes
+        {-100, 100, 0},
+        {100, -100, 0},
+        {-100, -100, 0},
+
+        // Test mipmaps with 0, 1, 2 as dimensions
+        // (SkMipMap::Build requires a min size of 2)
+        //
+        // 0
+        {0, 100, 0},
+        {100, 0, 0},
+        {0, 0, 0},
+        // 1
+        {1, 100, 0},
+        {100, 1, 0},
+        {1, 1, 0},
+        // 2
+        {2, 100, 1},
+        {100, 2, 1},
+        {2, 2, 1},
+
+        // Test a handful of boundaries such as 63x63 and 64x64
+        {63, 63, 5},
+        {64, 64, 6},
+        {127, 127, 6},
+        {128, 128, 7},
+        {255, 255, 7},
+        {256, 256, 8},
+
+        // Test different dimensions, such as 256x64
+        {64, 129, 6},
+        {255, 32, 5},
+        {500, 1000, 8}
+    };
+
+    for (auto& currentTest : tests) {
+        int levelCount = SkMipMap::ComputeLevelCount(currentTest.fWidth, currentTest.fHeight);
+        REPORTER_ASSERT(reporter, currentTest.fExpectedLevelCount == levelCount);
+    }
+}