summaryrefslogtreecommitdiff
path: root/src/blitter
diff options
context:
space:
mode:
authorJonathan G Rennison <j.g.rennison@gmail.com>2018-01-17 02:52:40 +0000
committerPeterN <peter@fuzzle.org>2019-01-24 11:12:06 +0000
commit4b256fed36f6edab42c6a18e5d31e17e38ac669b (patch)
treeb5cd69173762b2636bf234b9019f8f2e34727375 /src/blitter
parent0240e90169570f2ad2343c3cbbeade7886e599e9 (diff)
downloadopenttd-4b256fed36f6edab42c6a18e5d31e17e38ac669b.tar.xz
Codechange: [Blitter] Adjust line-drawing algorithm to reduce wasted off-screen work
This clips the line segment to be within the screen area prior to pixel iteration.
Diffstat (limited to 'src/blitter')
-rw-r--r--src/blitter/common.hpp76
1 files changed, 66 insertions, 10 deletions
diff --git a/src/blitter/common.hpp b/src/blitter/common.hpp
index 9019dd359..3e4911d00 100644
--- a/src/blitter/common.hpp
+++ b/src/blitter/common.hpp
@@ -15,6 +15,8 @@
#include "base.hpp"
#include "../core/math_func.hpp"
+#include <utility>
+
template <typename SetPixelT>
void Blitter::DrawLineGeneric(int x, int y, int x2, int y2, int screen_width, int screen_height, int width, int dash, SetPixelT set_pixel)
{
@@ -66,23 +68,50 @@ void Blitter::DrawLineGeneric(int x, int y, int x2, int y2, int screen_width, in
if (dash == 0) dash = 1;
int dash_count = 0;
if (dx > dy) {
+ if (stepx < 0) {
+ std::swap(x, x2);
+ std::swap(y, y2);
+ stepy = -stepy;
+ }
+ if (x2 < 0 || x >= screen_width) return;
+
int y_low = y;
int y_high = y;
int frac_low = dy - frac_diff / 2;
int frac_high = dy + frac_diff / 2;
- while (frac_low + dx / 2 < 0) {
+ while (frac_low < -(dx / 2)) {
frac_low += dx;
y_low -= stepy;
}
- while (frac_high - dx / 2 >= 0) {
+ while (frac_high >= dx / 2) {
frac_high -= dx;
y_high += stepy;
}
- x2 += stepx;
+
+ if (x < 0) {
+ dash_count = (-x) % (dash + gap);
+ auto adjust_frac = [&](int64 frac, int &y_bound) -> int {
+ frac -= ((int64) dy) * ((int64) x);
+ if (frac >= 0) {
+ int quotient = frac / dx;
+ int remainder = frac % dx;
+ y_bound += (1 + quotient) * stepy;
+ frac = remainder - dx;
+ }
+ return frac;
+ };
+ frac_low = adjust_frac(frac_low, y_low);
+ frac_high = adjust_frac(frac_high, y_high);
+ x = 0;
+ }
+ x2++;
+ if (x2 > screen_width) {
+ x2 = screen_width;
+ }
while (x != x2) {
- if (dash_count < dash && x >= 0 && x < screen_width) {
+ if (dash_count < dash) {
for (int y = y_low; y != y_high; y += stepy) {
if (y >= 0 && y < screen_height) set_pixel(x, y);
}
@@ -95,29 +124,56 @@ void Blitter::DrawLineGeneric(int x, int y, int x2, int y2, int screen_width, in
y_high += stepy;
frac_high -= dx;
}
- x += stepx;
+ x++;
frac_low += dy;
frac_high += dy;
if (++dash_count >= dash + gap) dash_count = 0;
}
} else {
+ if (stepy < 0) {
+ std::swap(x, x2);
+ std::swap(y, y2);
+ stepx = -stepx;
+ }
+ if (y2 < 0 || y >= screen_height) return;
+
int x_low = x;
int x_high = x;
int frac_low = dx - frac_diff / 2;
int frac_high = dx + frac_diff / 2;
- while (frac_low + dy / 2 < 0) {
+ while (frac_low < -(dy / 2)) {
frac_low += dy;
x_low -= stepx;
}
- while (frac_high - dy / 2 >= 0) {
+ while (frac_high >= dy / 2) {
frac_high -= dy;
x_high += stepx;
}
- y2 += stepy;
+
+ if (y < 0) {
+ dash_count = (-y) % (dash + gap);
+ auto adjust_frac = [&](int64 frac, int &x_bound) -> int {
+ frac -= ((int64) dx) * ((int64) y);
+ if (frac >= 0) {
+ int quotient = frac / dy;
+ int remainder = frac % dy;
+ x_bound += (1 + quotient) * stepx;
+ frac = remainder - dy;
+ }
+ return frac;
+ };
+ frac_low = adjust_frac(frac_low, x_low);
+ frac_high = adjust_frac(frac_high, x_high);
+ y = 0;
+ }
+ y2++;
+ if (y2 > screen_height) {
+ y2 = screen_height;
+ }
while (y != y2) {
- if (dash_count < dash && y >= 0 && y < screen_height) {
+ if (dash_count < dash) {
for (int x = x_low; x != x_high; x += stepx) {
if (x >= 0 && x < screen_width) set_pixel(x, y);
}
@@ -130,7 +186,7 @@ void Blitter::DrawLineGeneric(int x, int y, int x2, int y2, int screen_width, in
x_high += stepx;
frac_high -= dy;
}
- y += stepy;
+ y++;
frac_low += dx;
frac_high += dx;
if (++dash_count >= dash + gap) dash_count = 0;