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[Maintenance] [th01] graph_r_line(): Make slope calculations more explicit 

The previous macros suggested optimizations that could easily lead to
crashes.

Part of P0197, funded by Yanga and Ember2528.
This commit is contained in:
nmlgc 2022-05-31 09:05:32 +02:00
parent b4033b5fe4
commit b165871ece
1 changed files with 13 additions and 11 deletions
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24
th01/hardware/graph.cpp
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@ -519,24 +519,22 @@ void graph_r_line(
vram_y_t y_vram;
dots16_t pixels;
#define slope_x ((bottom - top) / (right - left))
#define slope_y ((right - left) / (bottom - top))
#define lerp(m, x) static_cast<int>(m * static_cast<float>(x))
#define clip_lerp_min(low, high, lerp_point, slope, minimum) \
#define clip_lerp_min(low, high, lerp_point, slope_dividend, minimum) \
if(low < minimum) { \
if(high < minimum) { \
return; \
} \
lerp_point += lerp(slope, (minimum - low)); \
lerp_point += lerp((slope_dividend / (high - low)), (minimum - low)); \
low = minimum; \
}
#define clip_lerp_max(low, high, lerp_point, slope, maximum) \
#define clip_lerp_max(low, high, lerp_point, slope_dividend, maximum) \
if(high > maximum) { \
if(low > maximum) { \
return; \
} \
lerp_point -= lerp(slope, (high - maximum)); \
lerp_point -= lerp((slope_dividend / (high - low)), (high - maximum)); \
high = maximum; \
}
@ -596,10 +594,14 @@ void graph_r_line(
bottom = order_tmp;
}
clip_lerp_min(left, right, top, slope_x, 0);
clip_lerp_max(left, right, bottom, slope_x, (RES_X - 1));
clip_lerp_min(top, bottom, left, slope_y, 0);
clip_lerp_max(top, bottom, right, slope_y, (RES_Y - 1));
clip_lerp_min(left, right, top, (bottom - top), 0);
clip_lerp_max(left, right, bottom, (bottom - top), (RES_X - 1));
clip_lerp_min(top, bottom, left, (right - left), 0);
clip_lerp_max(top, bottom, right, (right - left), (RES_Y - 1));
// This division is safe at this point.
#define slope_y ((right - left) / (bottom - top))
if(bottom < 0) {
right += lerp(slope_y, 0 - bottom);
bottom = 0;
@ -639,7 +641,7 @@ end:
#undef unput32_at
#undef clip_lerp_min
#undef clip_lerp_max
#undef slope
#undef slope_x
}
/// -----------------------