From 6465b086e7846835ff80d416d6a89ff90de4559c Mon Sep 17 00:00:00 2001
From: Niels Martin Hansen <nielsm@aegisub.org>
Date: Wed, 29 Aug 2007 18:40:51 +0000
Subject: [PATCH] Attempt to add some documentation for what Rasterizer::Draw
does.
Originally committed to SVN as r1541.
---
vsfilter/subtitles/Rasterizer.cpp | 54 ++++++++++++++++++++++++++++++-
1 file changed, 53 insertions(+), 1 deletion(-)
diff --git a/vsfilter/subtitles/Rasterizer.cpp b/vsfilter/subtitles/Rasterizer.cpp
index 40e5eda12..8860fcb9b 100644
--- a/vsfilter/subtitles/Rasterizer.cpp
+++ b/vsfilter/subtitles/Rasterizer.cpp
@@ -819,10 +819,19 @@ static __forceinline void pixmix_sse2(DWORD* dst, DWORD color, DWORD alpha)
*dst = (DWORD)_mm_cvtsi128_si32(r);
}
+// For CPUID usage in Rasterizer::Draw
#include "../dsutil/vd.h"
static const __int64 _00ff00ff00ff00ff = 0x00ff00ff00ff00ffi64;
+// Render a subpicture onto a surface.
+// spd is the surface to render on.
+// clipRect is a rectangular clip region to render inside.
+// pAlphaMask is an alpha clipping mask.
+// xsub and ysub ???
+// switchpts seems to be an array of interlaced colour switching coordinates/colours to switch to.
+// fBody tells whether to render the body of the subs.
+// fBorder tells whether to render the border of the subs.
CRect Rasterizer::Draw(SubPicDesc& spd, CRect& clipRect, byte* pAlphaMask, int xsub, int ysub, const long* switchpts, bool fBody, bool fBorder)
{
CRect bbox(0, 0, 0, 0);
@@ -831,20 +840,26 @@ CRect Rasterizer::Draw(SubPicDesc& spd, CRect& clipRect, byte* pAlphaMask, int x
// clip
+ // Limit drawn area to intersection of rendering surface and rectangular clip area
CRect r(0, 0, spd.w, spd.h);
r &= clipRect;
+ // Remember that all subtitle coordinates are specified in 1/8 pixels
+ // (x+4)>>3 rounds to nearest whole pixel.
+ // ??? What is xsub, ysub, mOffsetX and mOffsetY ?
int x = (xsub + mOffsetX + 4)>>3;
int y = (ysub + mOffsetY + 4)>>3;
int w = mOverlayWidth;
int h = mOverlayHeight;
int xo = 0, yo = 0;
+ // Again, limiting?
if(x < r.left) {xo = r.left-x; w -= r.left-x; x = r.left;}
if(y < r.top) {yo = r.top-y; h -= r.top-y; y = r.top;}
if(x+w > r.right) w = r.right-x;
if(y+h > r.bottom) h = r.bottom-y;
+ // Check if there's actually anything to render
if(w <= 0 || h <= 0) return(bbox);
bbox.SetRect(x, y, x+w, y+h);
@@ -852,25 +867,35 @@ CRect Rasterizer::Draw(SubPicDesc& spd, CRect& clipRect, byte* pAlphaMask, int x
// draw
+ // The alpha bitmap of the subtitles?
const byte* src = mpOverlayBuffer + 2*(mOverlayWidth * yo + xo);
const byte* s = fBorder ? (src+1) : src;
+ // The complex "vector clip mask" I think.
const byte* am = pAlphaMask + spd.w * y + x;
+ // How would this differ from src?
unsigned long* dst = (unsigned long *)((char *)spd.bits + spd.pitch * y) + x;
+ // ??? What is switchpts ?
unsigned long color = switchpts[0];
+ // CPUID from VDub
bool fSSE2 = !!(g_cpuid.m_flags & CCpuID::sse2);
+ // Every remaining line in the bitmap to be rendered...
while(h--)
{
+ // Basic case of no complex clipping mask
if(!pAlphaMask)
{
+ // Again, what is switchpts?
if(switchpts[1] == 0xffffffff)
{
+ // Are we rendering the fill or a border/shadow? I think...
if(fBody)
{
- const byte* s = fBorder?(src+1):src;
+ // Old code
/*
+ const byte* s = fBorder?(src+1):src;
for(int wt=0; wt<w; ++wt)
{
pixmix(s[wt*2]);
@@ -917,13 +942,19 @@ CRect Rasterizer::Draw(SubPicDesc& spd, CRect& clipRect, byte* pAlphaMask, int x
add edi, 4
loop pixmixloop
}*/
+ // Run over every pixel, overlaying the subtitles with the fill colour
if(fSSE2)
for(int wt=0; wt<w; ++wt)
+ // Why s[wt*2] and not s[wt] ?
+ // The <<6 is due to pixmix expecting the alpha parameter to be
+ // the multiplication of two 6-bit unsigned numbers but we
+ // only have one here. (No alpha mask.)
pixmix_sse2(&dst[wt], color, s[wt*2]<<6);
else
for(int wt=0; wt<w; ++wt)
pixmix(&dst[wt], color, s[wt*2]<<6);
}
+ // Not body, ie. something else (border, shadow, I guess)
else
{
/* for(int wt=0; wt<w; ++wt)
@@ -975,6 +1006,14 @@ CRect Rasterizer::Draw(SubPicDesc& spd, CRect& clipRect, byte* pAlphaMask, int x
}*/
if(fSSE2)
for(int wt=0; wt<w; ++wt)
+ // It would seems src (not s here?) contains two different
+ // bitmaps interlaced per pixel.
+ // So here's using the difference between those two.
+ // What if the difference underflows??
+ // I guess src[wt*2+1] is the widened region for border
+ // created by CreateWidenedRegion, and thus contains
+ // both the fill and the border, so subtracting the fill
+ // from that is always safe.
pixmix_sse2(&dst[wt], color, (src[wt*2+1] - src[wt*2])<<6);
else
for(int wt=0; wt<w; ++wt)
@@ -982,8 +1021,10 @@ CRect Rasterizer::Draw(SubPicDesc& spd, CRect& clipRect, byte* pAlphaMask, int x
}
//__asm emms;
}
+ // not (switchpts[1] == 0xffffffff)
else
{
+ // switchpts plays an important rule here
const long *sw = switchpts;
if(fBody)
@@ -1003,6 +1044,9 @@ CRect Rasterizer::Draw(SubPicDesc& spd, CRect& clipRect, byte* pAlphaMask, int x
if(fSSE2)
for(int wt=0; wt<w; ++wt)
{
+ // xo is the offset (usually negative) we have moved into the image
+ // So if we have passed the switchpoint (?) switch to another colour
+ // (So switchpts stores both colours *and* coordinates?)
if(wt+xo >= sw[1]) {while(wt+xo >= sw[1]) sw += 2; color = sw[-2];}
pixmix_sse2(&dst[wt], color, s[wt*2]<<6);
}
@@ -1013,6 +1057,7 @@ CRect Rasterizer::Draw(SubPicDesc& spd, CRect& clipRect, byte* pAlphaMask, int x
pixmix(&dst[wt], color, s[wt*2]<<6);
}
}
+ // Not body
else
{
/*for(int wt=0; wt<w; ++wt)
@@ -1040,6 +1085,7 @@ CRect Rasterizer::Draw(SubPicDesc& spd, CRect& clipRect, byte* pAlphaMask, int x
}
}
}
+ // Here we *do* have an alpha mask
else
{
if(switchpts[1] == 0xffffffff)
@@ -1054,6 +1100,11 @@ CRect Rasterizer::Draw(SubPicDesc& spd, CRect& clipRect, byte* pAlphaMask, int x
}*/
if(fSSE2)
for(int wt=0; wt<w; ++wt)
+ // Both s and am contain 6-bit bitmaps of two different
+ // alpha masks; s is the subtitle shape and am is the
+ // clipping mask.
+ // Multiplying them together yields a 12-bit number.
+ // I think some imprecision is introduced here??
pixmix_sse2(&dst[wt], color, s[wt*2] * am[wt]);
else
for(int wt=0; wt<w; ++wt)
@@ -1144,6 +1195,7 @@ CRect Rasterizer::Draw(SubPicDesc& spd, CRect& clipRect, byte* pAlphaMask, int x
}
}
+ // Step to next scanline
src += 2*mOverlayWidth;
s += 2*mOverlayWidth;
am += spd.w;
--
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