This exercise is programming problem 15.16 from the text: (Two movable vertices

Question

This exercise is programming problem 15.16 from the text:

(Two movable vertices and their distances) Write a program that displays two circles with radius 10 at location (40, 40) and (120, 150) with a line connecting the two circles, as shown in Figure 15.28b. The distance between the circles is displayed along the line. The user can drag a circle. When that happens, the circle and its line are moved and the distance between the circles is updated.

Explanation / Answer

float physicsProcessCollisionBetweenSelfAndActorRect(SPhysics *self, SPhysics *actor) { float diff = 99999; SVector relative_position_of_circle = getDifference2DBetweenVectors(&self->worldPosition, &actor->worldPosition); rotateVector2DBy(&relative_position_of_circle, -actor->axis.angleZ); // This aligns the coord system so the rect becomes an AABB float x_clamped_within_rectangle = relative_position_of_circle.x; float y_clamped_within_rectangle = relative_position_of_circle.y; LIMIT(x_clamped_within_rectangle, actor->physicsRect.l, actor->physicsRect.r); LIMIT(y_clamped_within_rectangle, actor->physicsRect.b, actor->physicsRect.t); // Calculate the distance between the circle's center and this closest point float distance_to_nearest_edge_x = relative_position_of_circle.x - x_clamped_within_rectangle; float distance_to_nearest_edge_y = relative_position_of_circle.y - y_clamped_within_rectangle; // If the distance is less than the circle's radius, an intersection occurs float distance_sq_x = SQUARE(distance_to_nearest_edge_x); float distance_sq_y = SQUARE(distance_to_nearest_edge_y); float radius_sq = SQUARE(self->physicsRadius); if(distance_sq_x + distance_sq_y physicsRect.r - actor->physicsRect.l) * 0.5f; float half_rect_h = (actor->physicsRect.t - actor->physicsRect.b) * 0.5f; CREATE_VECTOR(push_vector); // If we're at one of the corners of this object, treat this as a circular/circular collision if(fabs(relative_position_of_circle.x) > half_rect_w && fabs(relative_position_of_circle.y) > half_rect_h) { SVector edges; if(relative_position_of_circle.x > 0) edges.x = half_rect_w; else edges.x = -half_rect_w; if(relative_position_of_circle.y > 0) edges.y = half_rect_h; else edges.y = -half_rect_h; push_vector = relative_position_of_circle; moveVectorByInverseVector2D(&push_vector, &edges); // We now have the vector from the corner of the rect to the point. float delta_length = getVector2DMagnitude(&push_vector); float diff = self->physicsRadius - delta_length; // Find out how far away we are from our ideal distance // Normalise the vector push_vector.x /= delta_length; push_vector.y /= delta_length; scaleVector2DBy(&push_vector, diff); // Now multiply it by the difference push_vector.z = 0; } else // Nope - just bouncing against one of the edges { if(relative_position_of_circle.x > 0) // Ball is to the right push_vector.x = (half_rect_w + self->physicsRadius) - relative_position_of_circle.x; else push_vector.x = -((half_rect_w + self->physicsRadius) + relative_position_of_circle.x); if(relative_position_of_circle.y > 0) // Ball is above push_vector.y = (half_rect_h + self->physicsRadius) - relative_position_of_circle.y; else push_vector.y = -((half_rect_h + self->physicsRadius) + relative_position_of_circle.y); if(fabs(push_vector.x)

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