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Clarify some of the SIMD comments

This commit is contained in:
doyle 2020-07-05 01:49:40 +10:00
parent cc75695dc3
commit 5318693f48
1 changed files with 27 additions and 19 deletions
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46
RaylibSIMD.h
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@ -284,26 +284,33 @@ void RaylibSIMD_ImageDraw(Image *dst, Image src, Rectangle srcRec, Rectangle dst
if (srcPtr->format == UNCOMPRESSED_R8G8B8)
{
// NOTE: We load 4 pixels x 4 colors at a time. But if the
// source image is 3BPP, then the 4th color loaded in each
// source image is RGB, then the 4th color loaded in each
// pixel is going to be the RED component of the next pixel.
//
// Pixels[] = {RGB, RGB, RGB, RGB, ...}
//
// For example, naively loading the next 4 color components
// in a 3BPP byte stream, produces
// For example, naively loading the next pixels in a 3BPP
// byte stream, produces in a 128 bit SIMD register
//
// RGBR GBRG BRGB
// Pixel | 1 2 3 4
// Color | RGBR GBRG BRGB RGBR
// ^
// |
// +---- This is the 2nd pixel's Red Component
//
// The subsequent pixel needs to re-load the red channel
// to correctly pull the RGB components out and so forth for
// The subsequent pixels needs to shift the color channels
// to correctly set up the RGB components and so forth for
// subsequent pixels.
//
// RGBR RGBR RGBR
// Pixel | 1 2 3 4
// Color | RGBR RGBR RGBR RGBR
//
// We do this by shuffling the loaded bits into place
// duplicating the red channel and copying onwards. In the
// RGBA case, we do a no-op shuffle that preserves positions
// of all color components to avoid branches in the blitting
// hot path.
//
// We do this by shuffling the loaded pixels into place. In
// the 4BPP case, we do a no-op shuffle that preserves
// positions of all color components to avoid branches in
// the blitting hot path.
src_alpha_min = 255.f;
src_pixels_shuffle = _mm_set_epi8(12, 11, 10, 9, 9, 8, 7, 6, 6, 5, 4, 3, 3, 2, 1, 0);
}
@ -333,7 +340,7 @@ void RaylibSIMD_ImageDraw(Image *dst, Image src, Rectangle srcRec, Rectangle dst
dest_ptr += (SIMD_WIDTH * bytesPerPixelDst);
// NOTE: Unpack Source & Dest Pixel Layout for SIMD
// From {RGBA0, RGBA1, RGBA2, RGBA3} to {RRRR} {GGGG} {BBBB} {AAAA} where each
// From {ABGR1, ABGR2, ABGR3, ABGR3} to {RRRR} {GGGG} {BBBB} {AAAA} where each
// new {...} is one SIMD register with u32x4 lanes of the same color component.
//
// 1. Shift colour component to lowest 8 bits
@ -407,14 +414,15 @@ void RaylibSIMD_ImageDraw(Image *dst, Image src, Rectangle srcRec, Rectangle dst
__m128i blended0123_b_int = _mm_cvtps_epi32(blend0123_b);
// NOTE: Repack The Pixel
// From {RRRR} {GGGG} {BBBB} {AAAA} to {RGBA RGBA RGBA RGBA}
// i.e. blended0123_r_int = {[0,0,0,R], [0,0,0,R], [0,0,0,R], [0,0,0,R]}
// blended0123_g_int = {[0,0,0,G], [0,0,0,G], [0,0,0,G], [0,0,0,G]}
// ....
//
// Each blend has the color component converted to 8 bits sitting in the low bits of the register.
// From {RRRR} {GGGG} {BBBB} {AAAA} to {ABGR ABGR ABGR ABGR}
// Each blend has the color component converted to 8 bits sitting in the low bits of the SIMD lane.
// Shift the colors into place and or them together to get the final output
// pixel0123 = {[R,G,B,A], [R,G,B,A], [R,G,B,A], [R,G,B,A]}
//
// blended0123_r_int = {[0,0,0,R], [0,0,0,R], [0,0,0,R], [0,0,0,R]}
// blended0123_g_int = {[0,0,0,G], [0,0,0,G], [0,0,0,G], [0,0,0,G]}
// blended0123_b_int = {[0,0,0,B], [0,0,0,B], [0,0,0,B], [0,0,0,B]}
// blended0123_b_int = {[0,0,0,A], [0,0,0,A], [0,0,0,A], [0,0,0,A]}
// pixel0123 = {[A,B,G,R], [A,B,G,R], [A,B,G,R], [A,B,G,R]}
//
__m128i pixel0123 =
_mm_or_si128(blended0123_r_int,