Compute slope considering filtering, mirror.

BUG=261
TEST=valgrind
R=tpsiaki@google.com

Review URL: https://webrtc-codereview.appspot.com/5199004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@896 16f28f9a-4ce2-e073-06de-1de4eb20be90

README.chromium

 Name: libyuv
 URL: http://code.google.com/p/libyuv/
-Version: 895
+Version: 896
 License: BSD
 License File: LICENSE
 

include/libyuv/scale_row.h

@@ -55,10 +55,6 @@ extern "C" {
 #define HAS_SCALEROWDOWN38_MIPS_DSPR2
 #endif
 
-FilterMode ScaleFilterReduce(int src_width, int src_height,
-                             int dst_width, int dst_height,
-                             FilterMode filtering);
-
 // Scale ARGB vertically with bilinear interpolation.
 void ScalePlaneVertical(int src_height,
                         int dst_width, int dst_height,
@@ -67,6 +63,17 @@ void ScalePlaneVertical(int src_height,
                         int x, int y, int dy,
                         int bpp, FilterMode filtering);
 
+// Simplify the filtering based on scale factors.
+FilterMode ScaleFilterReduce(int src_width, int src_height,
+                             int dst_width, int dst_height,
+                             FilterMode filtering);
+
+// Compute slope values for stepping.
+void ScaleSlope(int src_width, int src_height,
+                int dst_width, int dst_height,
+                FilterMode filtering,
+                int* x, int* y, int* dx, int* dy);
+
 void ScaleRowDown2_C(const uint8* src_ptr, ptrdiff_t /* src_stride */,
                      uint8* dst, int dst_width);
 void ScaleRowDown2Linear_C(const uint8* src_ptr, ptrdiff_t src_stride,

include/libyuv/version.h

@@ -11,6 +11,6 @@
 #ifndef INCLUDE_LIBYUV_VERSION_H_  // NOLINT
 #define INCLUDE_LIBYUV_VERSION_H_
 
-#define LIBYUV_VERSION 895
+#define LIBYUV_VERSION 896
 
 #endif  // INCLUDE_LIBYUV_VERSION_H_  NOLINT

source/scale_argb.cc

@@ -593,33 +593,8 @@ static void ScaleARGB(const uint8* src, int src_stride,
   int dy = 0;
   int x = 0;
   int y = 0;
-  if (filtering) {
-    // Scale step for bilinear sampling renders last pixel once for upsample.
-    if (dst_width <= Abs(src_width)) {
-      dx = FixedDiv(Abs(src_width), dst_width);
-      x = (dx >> 1) - 32768;
-    } else if (dst_width > 1) {
-      dx = FixedDiv(Abs(src_width) - 1, dst_width - 1);
-    }
-    if (dst_height <= src_height) {
-      dy = FixedDiv(src_height,  dst_height);
-      y = (dy >> 1) - 32768;
-    } else if (dst_height > 1) {
-      dy = FixedDiv(src_height - 1, dst_height - 1);
-    }
-  } else {
-    // Scale step for point sampling duplicates all pixels equally.
-    dx = FixedDiv(Abs(src_width), dst_width);
-    dy = FixedDiv(src_height, dst_height);
-    x = dx >> 1;
-    y = dy >> 1;
-  }
-  // Negative src_width means horizontally mirror.
-  if (src_width < 0) {
-    x += (dst_width - 1) * dx;
-    dx = -dx;
-    src_width = -src_width;
-  }
+  ScaleSlope(src_width, src_height, dst_width, dst_height, filtering,
+             &dx, &dy, &x, &y);
   if (clip_x) {
     x += clip_x * dx;
     dst += clip_x * 4;

source/scale_common.cc

@@ -534,7 +534,7 @@ void ScalePlaneVertical(int src_height,
   }
 }
 
-// Scale plane vertically with bilinear interpolation.
+// Simplify the filtering based on scale factors.
 FilterMode ScaleFilterReduce(int src_width, int src_height,
                              int dst_width, int dst_height,
                              FilterMode filtering) {
@@ -575,6 +575,73 @@ FilterMode ScaleFilterReduce(int src_width, int src_height,
   return filtering;
 }
 
+#define CENTERSTART(dx, s) (dx < 0) ? -((-dx >> 1) + s) : ((dx >> 1) + s)
+#define FIXEDDIV1(src, dst) FixedDiv((src << 16) - 0x00010001, \
+                                     (dst << 16) - 0x00010001);
+
+// Compute slope values for stepping.
+void ScaleSlope(int src_width, int src_height,
+                int dst_width, int src_height,
+                FilterMode filtering,
+                int* x, int* y, int* dx, int* dy) {
+  assert(x != NULL);
+  assert(y != NULL);
+  assert(dx != NULL);
+  assert(dy != NULL);
+  assert(src_width != 0);
+  assert(src_height != 0);
+  assert(dst_width > 0);
+  assert(dst_height > 0);
+  if (filtering == kFilterBox) {
+    // Scale step for point sampling duplicates all pixels equally.
+    *dx = FixedDiv(Abs(src_width), dst_width);
+    *dy = FixedDiv(src_height, dst_height);
+    *x = 0;
+    *y = 0;
+  } else if (filtering == kFilterBilinear) {
+    // Scale step for bilinear sampling renders last pixel once for upsample.
+    if (dst_width <= Abs(src_width)) {
+      *dx = FixedDiv(Abs(src_width), dst_width);
+      *x = CENTERSTART(*dx, -32768);
+    } else if (dst_width > 1) {
+      *dx = FIXEDDIV1(Abs(src_width), dst_width);
+      *x = 0;
+    }
+    if (dst_height <= src_height) {
+      *dy = FixedDiv(src_height,  dst_height);
+      *y = CENTERSTART(*dy, -32768);
+    } else if (dst_height > 1) {
+      *dy = FIXEDDIV1(src_height, dst_height);
+      *y = 0;
+    }
+  } else if (filtering == kFilterLinear) {
+    // Scale step for bilinear sampling renders last pixel once for upsample.
+    if (dst_width <= Abs(src_width)) {
+      *dx = FixedDiv(Abs(src_width), dst_width);
+      *x = CENTERSTART(*dx, -32768);
+    } else if (dst_width > 1) {
+      *dx = FIXEDDIV1(Abs(src_width), dst_width);
+      *x = 0;
+    }
+    *dy = FixedDiv(src_height, dst_height);
+    *y = *dy >> 1;
+  } else {
+    // Scale step for point sampling duplicates all pixels equally.
+    *dx = FixedDiv(Abs(src_width), dst_width);
+    *dy = FixedDiv(src_height, dst_height);
+    *x = CENTERSTART(*dx, 0);
+    *y = CENTERSTART(*dy, 0);
+  }
+  // Negative src_width means horizontally mirror.
+  if (src_width < 0) {
+    *x += (dst_width - 1) * dx;
+    *dx = -*dx;
+    src_width = -src_width;
+  }
+}
+#undef CENTERSTART
+#undef FIXEDDIV1
+
 #ifdef __cplusplus
 }  // extern "C"
 }  // namespace libyuv