NEON shortcut for flat colour blending into 16-bit
This is a shortcut for the needs descriptor
00000077:03515104_00000000_00000000. It requires blending a single 32-bit
colour value into a 16-bit framebuffer.
It's used when fading out the screen, eg. when a modal requester pops-up.
The PF JIT produces code for this using 24 instructions/pixel. The NEON
implementation requires 2.1 instructions/pixel. Performance hasn't been
benchmarked, but the improvement is quite visible.
This code has only been tested by inspection of the fading effect described
above, when press+holding a finger on the home screen to pop up the
Shortcuts/Widgets/Folders/Wallpaper requester.
Along with the NEON version, a fallback v5TE implementation is also provided.
This ARM version of col32cb16blend is not fully optimised, but is a reasonable
implementation, and better than the version produced by the JIT. It is here as
a fallback, if NEON is not available.
diff --git a/libpixelflinger/col32cb16blend.S b/libpixelflinger/col32cb16blend.S
new file mode 100644
index 0000000..1450bde
--- /dev/null
+++ b/libpixelflinger/col32cb16blend.S
@@ -0,0 +1,78 @@
+/* libs/pixelflinger/col32cb16blend.S
+**
+** (C) COPYRIGHT 2009 ARM Limited.
+**
+** Licensed under the Apache License, Version 2.0 (the "License");
+** you may not use this file except in compliance with the License.
+** You may obtain a copy of the License at
+**
+** http://www.apache.org/licenses/LICENSE-2.0
+**
+** Unless required by applicable law or agreed to in writing, software
+** distributed under the License is distributed on an "AS IS" BASIS,
+** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+** See the License for the specific language governing permissions and
+** limitations under the License.
+**
+*/
+
+ .text
+ .align
+
+ .global scanline_col32cb16blend_arm
+
+//
+// This function alpha blends a fixed color into a destination scanline, using
+// the formula:
+//
+// d = s + (((a + (a >> 7)) * d) >> 8)
+//
+// where d is the destination pixel,
+// s is the source color,
+// a is the alpha channel of the source color.
+//
+
+// r0 = destination buffer pointer
+// r1 = color value
+// r2 = count
+
+
+scanline_col32cb16blend_arm:
+ push {r4-r10, lr} // stack ARM regs
+
+ mov r5, r1, lsr #24 // shift down alpha
+ mov r9, #0xff // create mask
+ add r5, r5, r5, lsr #7 // add in top bit
+ rsb r5, r5, #256 // invert alpha
+ and r10, r1, #0xff // extract red
+ and r12, r9, r1, lsr #8 // extract green
+ and r4, r9, r1, lsr #16 // extract blue
+ mov r10, r10, lsl #5 // prescale red
+ mov r12, r12, lsl #6 // prescale green
+ mov r4, r4, lsl #5 // prescale blue
+ mov r9, r9, lsr #2 // create dest green mask
+
+1:
+ ldrh r8, [r0] // load dest pixel
+ subs r2, r2, #1 // decrement loop counter
+ mov r6, r8, lsr #11 // extract dest red
+ and r7, r9, r8, lsr #5 // extract dest green
+ and r8, r8, #0x1f // extract dest blue
+
+ smlabb r6, r6, r5, r10 // dest red * alpha + src red
+ smlabb r7, r7, r5, r12 // dest green * alpha + src green
+ smlabb r8, r8, r5, r4 // dest blue * alpha + src blue
+
+ mov r6, r6, lsr #8 // shift down red
+ mov r7, r7, lsr #8 // shift down green
+ mov r6, r6, lsl #11 // shift red into 565
+ orr r6, r7, lsl #5 // shift green into 565
+ orr r6, r8, lsr #8 // shift blue into 565
+
+ strh r6, [r0], #2 // store pixel to dest, update ptr
+ bne 1b // if count != 0, loop
+
+ pop {r4-r10, pc} // return
+
+
+