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NUVIE: Fix Ultima 6 projectile collision

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Make the line drawing algorithm used in projectile collision detection
operate in screen space to match the original game.

Before this change the calculation was done in tile space, which caused
incorrect results.
This commit is contained in:
PushmePullyu 2023-03-23 04:03:57 +01:00 committed by Paul Gilbert
parent 1a7f516b18
commit de42667d75
1 changed files with 16 additions and 8 deletions
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24
engines/ultima/nuvie/core/map.cpp
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@ -762,16 +762,21 @@ bool Map::testIntersection(int x, int y, uint8 level, uint8 flags, LineTestResul
bool Map::lineTest(int start_x, int start_y, int end_x, int end_y, uint8 level,
uint8 flags, LineTestResult &Result, uint32 skip, Obj *excluded_obj) {
// standard Bresenham's algorithm.
int deltax = abs(end_x - start_x);
int deltay = abs(end_y - start_y);
// input tile coordinates are scaled up by 16 during line calculation
// and scaled back down before testing for collisions. this matches original
// game behaviour.
int deltax = abs(end_x - start_x) << 4;
int deltay = abs(end_y - start_y) << 4;
int x = start_x;
int y = start_y;
int x = (start_x << 4) + 8; // start at the center of the tile
int y = (start_y << 4) + 8;
int d;
int xinc1, xinc2;
int yinc1, yinc2;
int dinc1, dinc2;
uint32 count;
int xtile = start_x;
int ytile = start_y;
if (deltax >= deltay) {
@ -806,10 +811,6 @@ bool Map::lineTest(int start_x, int start_y, int end_x, int end_y, uint8 level,
}
for (uint32 i = 0; i < count; i++) {
// test the current location
if ((i >= skip) && (testIntersection(x, y, level, flags, Result, excluded_obj) == true))
return true;
if (d < 0) {
d += dinc1;
x += xinc1;
@ -819,6 +820,13 @@ bool Map::lineTest(int start_x, int start_y, int end_x, int end_y, uint8 level,
x += xinc2;
y += yinc2;
}
if( x >> 4 == xtile && y >> 4 == ytile)
continue; // we are still on the previous tile so skip the test
xtile = x >> 4;
ytile = y >> 4;
// test the current location
if ((i >= skip) && (testIntersection(xtile, ytile, level, flags, Result, excluded_obj) == true))
return true;
}
return false;