sforman
/
Thun
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Mostly working Wu-ish algorithm.

This commit is contained in:
Simon Forman 2023-02-27 16:29:45 -08:00
parent ee8ba58441
commit 300cf2f24d
2 changed files with 21 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
implementations/uvm-ncc/graphics.h
View File

@ -107,7 +107,7 @@ carefree_draw_box(u32* dest, size_t dest_stride, u64 y, u64 x, u64 w, u64 h, u32
void
plot_pixel(u32* dest, size_t dest_stride, u64 x, u64 y, u32 color, u8 alpha)
carefree_alpha_blend_plot_pixel(u32* dest, size_t dest_stride, u64 x, u64 y, u32 color, u8 alpha)
{
if (!alpha) return;
u32* pix_ptr = dest + dest_stride * y + x;
@ -127,29 +127,34 @@ plot_pixel(u32* dest, size_t dest_stride, u64 x, u64 y, u32 color, u8 alpha)
void
carefree_wu_line(u32* dest, size_t dest_stride, u64 x, u64 y, u64 w, u64 h, u32 color)
{
// Yeah... crunchy fun for the whole family.
// This isn't quite Wu's algorithm, although it uses the same
// fundamental trick of keeping track of both the intensity of
// the pixels to draw and the right time to increment the minor
// axis in a single error term.
//
// "An Efficient Antialiasing Technique", Xiaolin Wu
// Computer Graphics, Volume 25, Number 4, July 1991
// https://dl.acm.org/doi/pdf/10.1145/127719.122734
//
// "Graphics Programming Black Book" by Michael Abrash, chapter 42
// https://archive.org/details/gpbb20
// > Without loss of generality only lines in the first octant are considered.
assert(w > 0 && h > 0 && w >= h);
assert(w > 0 && h > 0 && w > h);
// > We translate the point (x0, y0) to the origin,
// so y = kx where k = h/w with k <= 1
u16 k = 0xFFFF * h / w;
u64 x1 = x + w - 1;
u64 y1 = y + h - 1;
u16 d = 0;
while (x1 > x) {
plot_pixel(dest, dest_stride, x, y + 1, color, d >> 8);
plot_pixel(dest, dest_stride, x, y, color, 0xFF - (d >> 8));
plot_pixel(dest, dest_stride, x1, y1, color, d >> 8);
plot_pixel(dest, dest_stride, x1, y1 + 1, color, 0xFF - (d >> 8));
u16 d = k >> 1;
while (w) {
w = w - 1;
u8 intensity = d >> 8;
carefree_alpha_blend_plot_pixel(dest, dest_stride, x, y + 1, color, intensity);
carefree_alpha_blend_plot_pixel(dest, dest_stride, x, y, color, 0xFF - intensity);
++x;
x1 = x1 - 1; // "--x1" didn't work here, x1 remained unchanged.
if (d + k >= 0xFFFF) {
d = 0;
d = k - (0xFFFF - d);
++y;
y1 = y1 - 1;
} else {
d = d + k;
}

2
implementations/uvm-ncc/xerblin.c
View File

@ -105,7 +105,7 @@ main()
u64 h = 4 + 4 * font_Inconsolata_22_height;
carefree_draw_box(frame_buffer, FRAME_WIDTH, 126, 126, w, h, WHITE);
w = 200;
//carefree_wu_line(frame_buffer, FRAME_WIDTH, 10, 256, 200, 100, WHITE);
carefree_wu_line(frame_buffer, FRAME_WIDTH, 0, 0, FRAME_WIDTH, FRAME_HEIGHT-1, WHITE);
//for (w = 101; w < (FRAME_WIDTH - 10); w = w + 50) {
// carefree_wu_line(frame_buffer, FRAME_WIDTH, 10, 256, w, 100, WHITE);
//}