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Fix assertion failure in triangle drawing on the SDL backend. #1437

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merged 1 commit into from
Jun 19, 2020
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Fix assertion failure in triangle drawing on the SDL backend. #1437

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34 changes: 18 additions & 16 deletions src/video/sdl/sdl_painter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -464,47 +464,49 @@ SDLPainter::draw_line(const LineRequest& request)

namespace {

Rectf
using Edge = std::pair<Vector, Vector>;

Edge
make_edge(int x1, int y1, int x2, int y2)
{
if (y1 < y2)
{
return Rectf(Vector(static_cast<float>(x1), static_cast<float>(y1)),
Vector(static_cast<float>(x2), static_cast<float>(y2)));
return Edge(Vector(static_cast<float>(x1), static_cast<float>(y1)),
Vector(static_cast<float>(x2), static_cast<float>(y2)));
}
else
{
return Rectf(Vector(static_cast<float>(x2), static_cast<float>(y2)),
Vector(static_cast<float>(x1), static_cast<float>(y1)));
return Edge(Vector(static_cast<float>(x2), static_cast<float>(y2)),
Vector(static_cast<float>(x1), static_cast<float>(y1)));
}
}

void
draw_span_between_edges(SDL_Renderer* renderer, const Rectf& e1, const Rectf& e2)
draw_span_between_edges(SDL_Renderer* renderer, const Edge& e1, const Edge& e2)
{
// calculate difference between the y coordinates
// of the first edge and return if 0
float e1ydiff = static_cast<float>(e1.get_bottom() - e1.get_top());
float e1ydiff = static_cast<float>(e1.second.y - e1.first.y);
if (e1ydiff == 0.0f)
return;

// calculate difference between the y coordinates
// of the second edge and return if 0
float e2ydiff = static_cast<float>(e2.get_bottom() - e2.get_top());
float e2ydiff = static_cast<float>(e2.second.y - e2.first.y);
if (e2ydiff == 0.0f)
return;

float e1xdiff = e1.get_right() - e1.get_left();
float e2xdiff = e2.get_right() - e2.get_left();
float factor1 = (e2.get_top() - e1.get_top()) / e1ydiff;
float e1xdiff = e1.second.x - e1.first.x;
float e2xdiff = e2.second.x - e2.first.x;
float factor1 = (e2.first.y - e1.first.y) / e1ydiff;
float factorStep1 = 1.0f / e1ydiff;
float factor2 = 0.0f;
float factorStep2 = 1.0f / e2ydiff;

for (int y = static_cast<int>(e2.get_top()); y < static_cast<int>(e2.get_bottom()); y++) {
for (int y = static_cast<int>(e2.first.y); y < static_cast<int>(e2.second.y); y++) {
SDL_RenderDrawLine(renderer,
static_cast<int>(e1.get_left() + e1xdiff * factor1), y,
static_cast<int>(e2.get_left() + e2xdiff * factor2), y);
static_cast<int>(e1.first.x + e1xdiff * factor1), y,
static_cast<int>(e2.first.x + e2xdiff * factor2), y);
factor1 += factorStep1;
factor2 += factorStep2;
}
Expand All @@ -527,7 +529,7 @@ SDLPainter::draw_triangle(const TriangleRequest& request)
int x3 = static_cast<int>(request.pos3.x);
int y3 = static_cast<int>(request.pos3.y);

Rectf edges[3];
Edge edges[3];
edges[0] = make_edge(x1, y1, x2, y2);
edges[1] = make_edge(x2, y2, x3, y3);
edges[2] = make_edge(x3, y3, x1, y1);
Expand All @@ -537,7 +539,7 @@ SDLPainter::draw_triangle(const TriangleRequest& request)

// find edge with the greatest length in the y axis
for (int i = 0; i < 3; i++) {
int length = static_cast<int>(edges[i].get_bottom() - edges[i].get_top());
int length = static_cast<int>(edges[i].second.y - edges[i].first.y);
if (length > maxLength) {
maxLength = length;
longEdge = i;
Expand Down