diff options
Diffstat (limited to 'generator/pamtris/boundaries.c')
| -rw-r--r-- | generator/pamtris/boundaries.c | 44 |
1 files changed, 40 insertions, 4 deletions
diff --git a/generator/pamtris/boundaries.c b/generator/pamtris/boundaries.c index 04237e59..e11ea894 100644 --- a/generator/pamtris/boundaries.c +++ b/generator/pamtris/boundaries.c @@ -1,12 +1,32 @@ +/*============================================================================= + boundaries.c +=============================================================================== + Boundary buffer functions + + New triangles are drawn one scanline at a time, and for every such scanline + we have left and right boundary columns within the frame buffer such that + the fraction of the triangle's area within that scanline is enclosed + between those two points (inclusive). Those coordinates may correspond to + columns outside the frame buffer's actual limits, in which case proper + post-processing should be made wherever such coordinates are used to + actually plot anything into the frame buffer. +=============================================================================*/ + #include <stdlib.h> -#include "common.h" +#include <netpbm/mallocvar.h> + +#include "utils.h" +#include "fract.h" + + +#include "boundaries.h" static fract make_pos_fract(int32_t const quotient, - int32_t const remainder) { + int32_t const remainder) { fract retval; @@ -39,7 +59,18 @@ gen_triangle_boundaries(int32_t xy[3][2], boundary_info * bi, int16_t width, int16_t height) { - +/*---------------------------------------------------------------------------- + Generate an entry in the boundary buffer for the boundaries of every + VISIBLE row of a particular triangle. In case there is no such row, + start_row is accordingly set to -1. The argument is a 3-element array + of pairs of int16_t's representing the coordinates of the vertices of + a triangle. Those vertices MUST be already sorted in order from the + uppermost to the lowermost vertex (which is what draw_triangle, the + only function which uses this one, does with the help of sort3). + + The return value indicates whether the middle vertex is to the left of the + line connecting the top vertex to the bottom vertex or not. +-----------------------------------------------------------------------------*/ int16_t leftmost_x = xy[0][0]; int16_t rightmost_x = xy[0][0]; int mid_is_to_the_left; @@ -277,7 +308,12 @@ get_triangle_boundaries(uint16_t row_index, int32_t * left, int32_t * right, const boundary_info * bi) { - +/*---------------------------------------------------------------------------- + Return the left and right boundaries for a given VISIBLE triangle row (the + row index is relative to the first visible row). These values may be out of + the horizontal limits of the frame buffer, which is necessary in order to + compute correct attribute interpolations. +-----------------------------------------------------------------------------*/ uint32_t i = row_index << 1; *left = bi->buffer[i]; |