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@ -148,16 +148,73 @@ struct GroundVehicle : public SpecializedVehicle<T, Type> {
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/**
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* Updates vehicle's Z position.
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* Inclination can't change in the middle of a tile.
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* The faster code is used for trains and road vehicles unless they are
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* reversing on a sloped tile.
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*/
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FORCEINLINE void UpdateZPosition()
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{
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/* Vehicle's Z position can change only if it has GVF_GOINGUP_BIT or GVF_GOINGDOWN_BIT set */
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#if 0
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/* The following code does this: */
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if (HasBit(this->gv_flags, GVF_GOINGUP_BIT)) {
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switch (this->direction) {
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case DIR_NE:
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this->z_pos += (this->x_pos & 1); break;
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case DIR_SW:
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this->z_pos += (this->x_pos & 1) ^ 1; break;
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case DIR_NW:
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this->z_pos += (this->y_pos & 1); break;
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case DIR_SE:
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this->z_pos += (this->y_pos & 1) ^ 1; break;
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default: break;
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}
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} else if (HasBit(this->gv_flags, GVF_GOINGDOWN_BIT)) {
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switch (this->direction) {
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case DIR_NE:
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this->z_pos -= (this->x_pos & 1); break;
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case DIR_SW:
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this->z_pos -= (this->x_pos & 1) ^ 1; break;
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case DIR_NW:
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this->z_pos -= (this->y_pos & 1); break;
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case DIR_SE:
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this->z_pos -= (this->y_pos & 1) ^ 1; break;
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default: break;
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}
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}
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/* But gcc 4.4.5 isn't able to nicely optimise it, and the resulting
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* code is full of conditional jumps. */
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#endif
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/* Vehicle's Z position can change only if it has GVF_GOINGUP_BIT or GVF_GOINGDOWN_BIT set.
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* Furthermore, if this function is called once every time the vehicle's position changes,
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* we know the Z position changes by +/-1 at certain moments - when x_pos, y_pos is odd/even,
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* depending on orientation of the slope and vehicle's direction */
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if (HasBit(this->gv_flags, GVF_GOINGUP_BIT) || HasBit(this->gv_flags, GVF_GOINGDOWN_BIT)) {
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this->z_pos = GetSlopeZ(this->x_pos, this->y_pos);
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} else {
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/* Verify that assumption. */
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assert(this->z_pos == GetSlopeZ(this->x_pos, this->y_pos));
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if (T::From(this)->HasToUseGetSlopeZ()) {
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/* In some cases, we have to use GetSlopeZ() */
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this->z_pos = GetSlopeZ(this->x_pos, this->y_pos);
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return;
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}
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/* DirToDiagDir() is a simple right shift */
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DiagDirection dir = DirToDiagDir(this->direction);
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/* Read variables, so the compiler knows the access doesn't trap */
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int8 x_pos = this->x_pos;
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int8 y_pos = this->y_pos;
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/* DiagDirToAxis() is a simple mask */
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int8 d = DiagDirToAxis(dir) == AXIS_X ? x_pos : y_pos;
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/* We need only the least significant bit */
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d &= 1;
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/* Conditional "^ 1". Optimised to "(dir - 1) <= 1". */
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d ^= (int8)(dir == DIAGDIR_SW || dir == DIAGDIR_SE);
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/* Subtraction instead of addition because we are testing for GVF_GOINGUP_BIT.
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* GVF_GOINGUP_BIT is used because it's bit 0, so simple AND can be used,
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* without any shift */
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this->z_pos += HasBit(this->gv_flags, GVF_GOINGUP_BIT) ? d : -d;
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}
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assert(this->z_pos == GetSlopeZ(this->x_pos, this->y_pos));
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}
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/**
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