Fix rendering of fire effects when their intensity exceeds 1.0f

This had been overlooked for a long time because intensity defaults to 1.0f and is seldom changed. The underlying issue is that an intensity value higher than 1.0f produces fire_alpha values above 255, which the new graphics code doesn't deal with properly. That said, that code works fine for every other case, so the solution is to add a special case for when fire_alpha is used.

src/graphics/Pixel.h

@@ -64,6 +64,16 @@ struct alignas(alignof(uint32_t) > alignof(T) ? alignof(uint32_t) : alignof(T))
 		);
 	}
 
+	template<typename S = T, typename = std::enable_if_t<std::is_same_v<S, uint8_t>>>
+	constexpr RGB<T> AddFire(RGB<T> other, int fireAlpha) const
+	{
+		return RGB<T>(
+			std::min(0xFF, Red + (fireAlpha * other.Red) / 0xFF),
+			std::min(0xFF, Green + (fireAlpha * other.Green) / 0xFF),
+			std::min(0xFF, Blue + (fireAlpha * other.Blue) / 0xFF)
+		);
+	}
+
 	// Decrement each component that is nonzero.
 	template<typename S = T, typename = std::enable_if_t<std::is_same_v<S, uint8_t>>>
 	constexpr RGB<T> Decay() const

src/graphics/RasterDrawMethods.h

@@ -13,6 +13,7 @@ struct RasterDrawMethods
 	void DrawPixel(Vec2<int>, RGB<uint8_t>);
 	void BlendPixel(Vec2<int>, RGBA<uint8_t>);
 	void AddPixel(Vec2<int>, RGBA<uint8_t>);
+	void AddFirePixel(Vec2<int>, RGB<uint8_t>, int fireAlpha);
 	void XorPixel(Vec2<int>);
 
 	void DrawLine(Vec2<int>, Vec2<int>, RGB<uint8_t>);

src/graphics/RasterDrawMethodsImpl.h

@@ -55,6 +55,16 @@ inline void RasterDrawMethods<Derived>::AddPixel(Vec2<int> pos, RGBA<uint8_t> co
 	}
 }
 
+template<typename Derived>
+inline void RasterDrawMethods<Derived>::AddFirePixel(Vec2<int> pos, RGB<uint8_t> colour, int fireAlpha)
+{
+	if (clipRect().Contains(pos))
+	{
+		pixel &px = (static_cast<Derived &>(*this).video)[pos];
+		px = RGB<uint8_t>::Unpack(px).AddFire(colour, fireAlpha).Pack();
+	}
+}
+
 template<typename Derived>
 inline void RasterDrawMethods<Derived>::XorPixel(Vec2<int> pos)
 {

src/graphics/Renderer.cpp

@@ -1161,7 +1161,7 @@ void Renderer::render_fire()
 						a = fire_alpha[y+CELL][x+CELL];
 						if (findingElement)
 							a /= 2;
-						AddPixel({ i*CELL+x, j*CELL+y }, RGBA<uint8_t>(r, g, b, a));
+						AddFirePixel({ i*CELL+x, j*CELL+y }, RGB<uint8_t>(r, g, b), a);
 					}
 			r *= 8;
 			g *= 8;