How to use b2Draw with SDL2? DrawSegment is not called - c++

Question

I expect to see hello in the console:
DebugDrawer.cpp
#include "DebugDrawer.h"
#include <iostream>
DebugDrawer::DebugDrawer()
{
}
void DebugDrawer::DrawSegment(const b2Vec2 &p1, const b2Vec2 &p2, const b2Color &color)
{
std::cout << "hello" << std::endl;
}
void DebugDrawer::DrawSolidPolygon(const b2Vec2 *vertices, int32 vertexCount, const b2Color &color) { }
void DebugDrawer::DrawPolygon(const b2Vec2 *vertices, int32 vertexCount, const b2Color &color) { }
void DebugDrawer::DrawPoint(const b2Vec2 &p, float size, const b2Color &color) { }
void DebugDrawer::DrawCircle(const b2Vec2 &center, float radius, const b2Color &color) { }
void DebugDrawer::DrawSolidCircle(const b2Vec2 &center, float radius, const b2Vec2 &axis, const b2Color &color) { }
void DebugDrawer::DrawTransform(const b2Transform &xf) { }
I inherited from the b2Draw and overloaded the methods:
DebugDrawer.h
#ifndef DEBUGDRAWER_H
#define DEBUGDRAWER_H
#include "box2d/b2_draw.h"
class DebugDrawer : public b2Draw
{
public:
DebugDrawer();
private:
void DrawSolidPolygon(const b2Vec2* vertices, int32 vertexCount, const b2Color& color);
void DrawPoint (const b2Vec2 &p, float size, const b2Color &color);
void DrawPolygon(const b2Vec2* vertices, int32 vertexCount, const b2Color& color);
void DrawCircle(const b2Vec2& center, float radius, const b2Color& color);
void DrawSolidCircle(const b2Vec2& center, float radius, const b2Vec2& axis, const b2Color& color);
void DrawSegment(const b2Vec2& p1, const b2Vec2& p2, const b2Color& color);
void DrawTransform(const b2Transform& xf);
};
#endif // DEBUGDRAWER_H
I created an object with the box shape:
b2PolygonShape shape;
shape.SetAsBox(50.f / WORLD_SCALE, 50.f / WORLD_SCALE);
b2BodyDef bdef;
bdef.type = b2_staticBody;
pBody = pWorld->CreateBody(&bdef);
pBody->CreateFixture(&shape, 2.f);
I set the debug draw in the main.cpp file:
pDebugDrawer = new DebugDrawer();
pWorld->SetDebugDraw(pDebugDrawer);
I set flags:
uint32 flags = 0;
flags += b2Draw::e_shapeBit;
flags += b2Draw::e_jointBit;
flags += b2Draw::e_centerOfMassBit;
flags += b2Draw::e_aabbBit;
flags += b2Draw::e_pairBit;
pDebugDrawer->SetFlags(flags);
I call pWorld.Step() and pWorld->DebugDraw():
pWorld->Step(0.016f, 8, 3);
pWorld->DebugDraw();
main.cpp
#ifdef _WIN32
#include <windows.h>
extern "C" __declspec(dllexport) DWORD NvOptimusEnablement = 0x00000001;
extern "C" __declspec(dllexport) DWORD AmdPowerXpressRequestHighPerformance = 0x00000001;
#endif
#define SDL_MAIN_HANDLED
#include <glad/glad.h>
#include <SDL.h>
#include <box2d/box2d.h>
#include <iostream>
#include "DebugDrawer.h"
const float WORLD_SCALE = 30.f;
b2World* pWorld;
DebugDrawer* pDebugDrawer;
b2Body* pBody;
int main()
{
// Initialize the SDL2 library
if (SDL_Init(SDL_INIT_VIDEO) != 0)
{
SDL_Log("Failed to initialize the SDL2 library: %s", SDL_GetError());
return 1;
}
// Create a SDL window
const int WIN_WIDTH = 500;
const int WIN_HEIGHT = 500;
SDL_Window* window = SDL_CreateWindow(
"Empty Window",
SDL_WINDOWPOS_CENTERED,
SDL_WINDOWPOS_CENTERED,
WIN_WIDTH, WIN_HEIGHT,
SDL_WINDOW_SHOWN | SDL_WINDOW_OPENGL);
// Create a SDL renderer
SDL_Renderer* renderer = SDL_CreateRenderer(
window, -1, SDL_RENDERER_ACCELERATED);
if (!renderer)
{
SDL_Log("Failed to create a SDL renderer %s", SDL_GetError());
return 1;
}
SDL_GLContext context = SDL_GL_CreateContext(window);
// Initialize the GLAD library
if (!gladLoadGL())
{
SDL_Log("Failed to initialize the GLAD library");
return 1;
}
glViewport(0, 0, WIN_WIDTH, WIN_HEIGHT);
glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
b2Vec2 gravity(0.f, 9.8f);
pWorld = new b2World(gravity);
pDebugDrawer = new DebugDrawer();
pWorld->SetDebugDraw(pDebugDrawer);
uint32 flags = 0;
flags += b2Draw::e_shapeBit;
flags += b2Draw::e_jointBit;
flags += b2Draw::e_centerOfMassBit;
flags += b2Draw::e_aabbBit;
flags += b2Draw::e_pairBit;
pDebugDrawer->SetFlags(flags);
b2PolygonShape shape;
shape.SetAsBox(50.f / WORLD_SCALE, 50.f / WORLD_SCALE);
b2BodyDef bdef;
bdef.type = b2_staticBody;
pBody = pWorld->CreateBody(&bdef);
pBody->CreateFixture(&shape, 2.f);
SDL_Event event;
bool running = true;
SDL_PollEvent(&event);
while (running)
{
switch (event.type)
{
case SDL_QUIT:
running = false;
break;
case SDL_KEYDOWN:
switch (event.key.keysym.sym)
{
case SDLK_ESCAPE:
running = false;
break;
}
break;
}
glClear(GL_COLOR_BUFFER_BIT);
pWorld->Step(0.016f, 8, 3);
pWorld->DebugDraw();
SDL_GL_SwapWindow(window);
SDL_PollEvent(&event);
}
delete pWorld;
delete pDebugDrawer;
SDL_GL_DeleteContext(context);
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
return 0;
}

Answer 1

I should use DrawPolygon to draw segments of colliders when I use boxes to draw borders around game objects. DrawSegment() will be called when an instance of b2EdgeShape is created:
b2EdgeShape edgeShape;
edgeShape.SetOneSided(b2Vec2(0.f, 0.f), b2Vec2(1.f, 0.f),
b2Vec2(2.f, 0.f), b2Vec2(3.f, 0.f));
m_pEdgeBody = m_pWorld->CreateBody(&bdef);
m_pEdgeBody->CreateFixture(&edgeShape, 2.f);