From bd9aba933b24e37bafb39a4b9a3afd3e846fb400 Mon Sep 17 00:00:00 2001 From: Anurag Thakur Date: Tue, 11 Oct 2022 04:47:58 +0530 Subject: [PATCH] Add comments to raster algorithm and cleanup --- src/dense/ftdense.c | 92 ++++++++++++++++++--------------------------- 1 file changed, 36 insertions(+), 56 deletions(-) diff --git a/src/dense/ftdense.c b/src/dense/ftdense.c index deae76a8c..c167a9688 100644 --- a/src/dense/ftdense.c +++ b/src/dense/ftdense.c @@ -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; }