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Add comments to raster algorithm and cleanup

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This commit is contained in:
Anurag Thakur 2022-10-11 04:47:58 +05:30
parent d257405687
commit bd9aba933b
1 changed files with 36 additions and 56 deletions
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92
src/dense/ftdense.c
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@ -83,36 +83,22 @@ swap( long int* a, long int* b )
void
dense_render_line( dense_worker* worker, TPos tox, TPos toy )
{
// printf("line from: %d, %d to %d, %d\n", worker->prev_x, worker->prev_y,
// to_x, to_y);
FT26D6 fx = worker->prev_x>>2;
FT26D6 fy = worker->prev_y>>2;
// float from_x = fx;
// float from_y = fy;
FT26D6 from_x = fx;
FT26D6 from_y = fy;
// from_x /= 64.0;
// from_y /= 64.0;
FT26D6 tx = tox>>2;
FT26D6 ty = toy>>2;
if ( fy == ty )
return;
// float to_x = tx / 64.0;
// float to_y = ty / 64.0;
FT26D6 to_x = tx;
FT26D6 to_y = ty;
// from_x/y and to_x/y are coordinates in 26.6 format
if ( from_y == to_y )
return;
//printf("line from: %f, %f to %f, %f\n", from_x, from_y, to_x, to_y);
@ -128,7 +114,7 @@ dense_render_line( dense_worker* worker, TPos tox, TPos toy )
if ( from_y >= worker->m_h<<6 || to_y <= 0 )
return;
//float dxdy = ( to_x - from_x ) / (float)( to_y - from_y );
FT26D6 deltax,deltay;
deltax = to_x - from_x;
deltay = to_y - from_y;
@ -139,26 +125,38 @@ dense_render_line( dense_worker* worker, TPos tox, TPos toy )
from_y = 0;
}
// TODO: test, imp line
// This condition is important apparently
if ( to_y > worker->m_h<<6 )
{
to_x -= (( to_y - worker->m_h<<6 ) * deltax/deltay);
to_y = worker->m_h<<6;
}
int x = from_x;
FT26D6 x = from_x;
// y-coordinate of first pixel of line
int y0 = from_y>>6;
// y-coordinate of last pixel of line
int y_limit = (to_y + 0x3f)>>6;
FT20D12* m_a = worker->m_a;
FT20D12* m_a = worker->m_a;
for ( int y = y0; y < y_limit; y++ )
{
// printf("y is %d\n", y);
int linestart = y * worker->m_w;
// dy is the height of the line present in the current scanline
FT26D6 dy = min( (y + 1)<<6, to_y ) - max( y<<6, from_y );
// x coordinate where the line leaves the current scanline
FT26D6 xnext = x + dy * deltax/deltay;
// height with sign
FT26D6 d = dy * dir;
// x0 is the x coordinate of the start of line in current scanline
// x1 is the x coordinate of the end of line in current scanline
FT26D6 x0, x1;
if ( x < xnext )
{
@ -171,48 +169,43 @@ dense_render_line( dense_worker* worker, TPos tox, TPos toy )
x1 = x;
}
/*
It's possible for x0 to be negative on the last scanline because of
floating-point inaccuracy That would cause an out-of-bounds array access at
index -1.
*/
// float x0floor = x0 <= 0.0f ? 0.0f : (float)floor( x0 );
// x coordinate of the leftmost intersected pixel in the scanline
int x0i = x0>>6;
FT26D6 x0floor = x0i<<6;
// float x1ceil = (float)ceil( x1 );
// x coordinate of the rightmost intersected pixel in the scanline
int x1i = (x1+0x3f)>>6;
FT26D6 x1ceil = x1i <<6;
if ( x1i <= x0i + 1 )
{
// average of x coordinates of trapezium with origin at left of pixel
FT26D6 xmf = ( ( x + xnext )>>1) - x0floor;
// average of x coordinates of trapezium with origin at right of pixel
m_a[linestart + x0i] += d * ((1<<6) - xmf);
m_a[linestart + ( x0i + 1 )] += d * xmf;
}
else
{
// float s = 1.0f / ( x1 - x0 );
// float x0f = x0 - x0floor;
// float a0 = 0.5f * s * ( 1.0f - x0f ) * ( 1.0f - x0f );
// float x1f = x1 - x1ceil + 1.0f;
// float am = 0.5f * s * x1f * x1f;
// total horizontal length of line in current scanline, might be replaced by deltax
FT26D6 oneOverS = x1 - x0;
FT26D6 x0f = x0 - x0floor;
// 64 - x0f is the horizontal length of line in first pixel
FT26D6 oneMinusX0f = (1<<6) - x0f;
// Stores area of triangle in first pixel divided by d
FT26D6 a0 = ((oneMinusX0f * oneMinusX0f) >> 1) / oneOverS;
// x1f is the horizontal length in the last pixel
FT26D6 x1f = x1 - x1ceil + (1<<6);
FT26D6 am = ((x1f * x1f) >> 1) / oneOverS;
// printf("x0 is %lld, x1 is %lld\n",x0,x1 );
// d * a0 is area of triangle in first pixel
m_a[linestart + x0i] += d * a0;
if ( x1i == x0i + 2 )
@ -224,12 +217,15 @@ dense_render_line( dense_worker* worker, TPos tox, TPos toy )
FT26D6 dTimesS = (d << 12) / oneOverS;
for ( FT26D6 xi = x0i + 2; xi < x1i - 1; xi++ )
for ( FT26D6 xi = x0i + 2; xi < x1i - 1; xi++ ){
// Increase area for successive pixels by dy/dx
m_a[linestart + xi] += dTimesS;
}
FT26D6 a2 = a1 + (( x1i - x0i - 3 )<<12)/oneOverS;
m_a[linestart + ( x1i - 1 )] += d * ( (1<<6) - a2 - am );
}
// Area in last pixel of scanline
m_a[linestart + x1i] += d * am;
}
x = xnext;
@ -459,22 +455,6 @@ dense_render_glyph( dense_worker* worker, const FT_Bitmap* target )
dest++;
}
// float value = 0.0f;
// while ( dest < dest_end )
// {
// value += *source++;
// if ( value > 0.0f )
// {
// int n = (int)( fabs( value ) * 255.0f + 0.5f );
// if ( n > 255 )
// n = 255;
// *dest = (unsigned char)n;
// }
// else
// *dest = 0;
// dest++;
// }
free(worker->m_a);
return error;
}