C++ SDL2 / Scrolling Collision Issue - c++

Question

As the title suggests, I am trying to implement collision with scrolling.
The code here isn't the tidiest and it doesn't make use of object-oriented programming. But this code is a prototype for collision in a game I am making so I can reuse in that game.
Anyway, when I wrote this code and implemented no scrolling, the collision worked fine. However, when I implemented scrolling, suddenly, one pixel of the rectangle that represent the player gets stuck in the rectangles I've used to test the collision.
Here's the code.
Main.cpp:
#include "SDL.h"
#include "SDL_image.h"
#include "SDL_mixer.h"
#include "SDL_ttf.h"
using namespace std;
int main(int argc, char *argv[]) {
SDL_Init(SDL_INIT_EVERYTHING);
IMG_Init(IMG_INIT_PNG | IMG_INIT_JPG);
Mix_Init(MIX_INIT_MP3);
Mix_OpenAudio(MIX_DEFAULT_FREQUENCY, MIX_DEFAULT_FORMAT, 2, 640);
TTF_Init();
SDL_Window *Window = SDL_CreateWindow("Test", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 1000, 600, SDL_WINDOW_SHOWN);
SDL_Renderer *Renderer = SDL_CreateRenderer(Window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
bool quit = false;
SDL_Event Event;
SDL_Rect Box;
Box.w = 25;
Box.h = 25;
Box.x = 500 - int(Box.w / 2);
Box.y = 300 - int(Box.h / 2);
int CAMERA_X = 0;
int CAMERA_Y = 0;
int xVel = 0;
int yVel = 0;
SDL_Rect RECTS[3];
RECTS[0].x = 50;
RECTS[0].y = 50;
RECTS[0].w = 50;
RECTS[0].h = 100;
RECTS[1].x = 150;
RECTS[1].y = 50;
RECTS[1].w = 50;
RECTS[1].h = 100;
RECTS[2].x = 250;
RECTS[2].y = 50;
RECTS[2].w = 50;
RECTS[2].h = 100;
SDL_Rect CAM_RECTS[3];
CAM_RECTS[0].x = 50;
CAM_RECTS[0].y = 50;
CAM_RECTS[0].w = 50;
CAM_RECTS[0].h = 100;
CAM_RECTS[1].x = 150;
CAM_RECTS[1].y = 50;
CAM_RECTS[1].w = 50;
CAM_RECTS[1].h = 100;
CAM_RECTS[2].x = 250;
CAM_RECTS[2].y = 50;
CAM_RECTS[2].w = 50;
CAM_RECTS[2].h = 100;
const Uint8 *Input = NULL;
while (!quit) {
Input = SDL_GetKeyboardState(NULL);
while (SDL_PollEvent(&Event)) {
if (Event.type == SDL_QUIT) {
quit = true;
}
}
if (Input[SDL_SCANCODE_RIGHT]) {
xVel = -7;
} else if (Input[SDL_SCANCODE_LEFT]) {
xVel = 7;
} else {
xVel = 0;
}
if (Input[SDL_SCANCODE_UP]) {
yVel = 7;
} else if (Input[SDL_SCANCODE_DOWN]) {
yVel = -7;
} else {
yVel = 0;
}
for (unsigned int i = 0; i < 3; i++) {
CAM_RECTS[i].x = RECTS[i].x + CAMERA_X;
CAM_RECTS[i].y = RECTS[i].y + CAMERA_Y;
}
CAMERA_X += xVel;
for (unsigned int i = 0; i < 3; i++) {
if (Box.x <= CAM_RECTS[i].x + CAM_RECTS[i].w && Box.x + Box.w >= CAM_RECTS[i].x && Box.y <= CAM_RECTS[i].y + CAM_RECTS[i].h && Box.y + Box.h >= CAM_RECTS[i].y) {
if (Box.x <= CAM_RECTS[i].x + CAM_RECTS[i].w && Box.x + Box.w >= CAM_RECTS[i].x) {
CAMERA_X += -xVel;
}
}
}
CAMERA_Y += yVel;
for (unsigned int i = 0; i < 3; i++) {
if (Box.x <= CAM_RECTS[i].x + CAM_RECTS[i].w && Box.x + Box.w >= CAM_RECTS[i].x && Box.y <= CAM_RECTS[i].y + CAM_RECTS[i].h && Box.y + Box.h >= CAM_RECTS[i].y) {
if (Box.y <= CAM_RECTS[i].y + CAM_RECTS[i].h && Box.y + Box.h >= CAM_RECTS[i].y) {
CAMERA_Y += -yVel;
}
}
}
SDL_SetRenderDrawColor(Renderer, 0, 0, 0, 255);
SDL_RenderClear(Renderer);
SDL_SetRenderDrawColor(Renderer, 255, 255, 255, 255);
SDL_RenderFillRect(Renderer, &Box);
SDL_SetRenderDrawColor(Renderer, 255, 255, 255, 255);
for (unsigned int i = 0; i < 3; i++) {
SDL_RenderFillRect(Renderer, &CAM_RECTS[i]);
}
SDL_RenderPresent(Renderer);
}
Input = NULL;
SDL_DestroyRenderer(Renderer);
SDL_DestroyWindow(Window);
TTF_Quit();
Mix_CloseAudio();
Mix_Quit();
IMG_Quit();
SDL_Quit();
return 0;
}
Please help.
Thank you very much :)

Answer 1

Ok, I changed answer, now it should work without jittering.
It's definitely not the best solution, but it would depends on wider concepion of your program.
int sign(int x)
{
return (x > 0) - (x < 0);
}
/* Movement values are updated by referenced arguments.*/
void check_collisions(SDL_Rect* obj_rects, unsigned num_of_obj,
SDL_Rect obstacle, int& horizontal_move, int& vertical_move)
{
for (unsigned int i = 0; i < num_of_obj; i++)
{
int obj_new_x = obj_rects[i].x + horizontal_move;
// Horizontal collision
if (obj_new_x < (obstacle.x + obstacle.w)
&& (obj_new_x + obj_rects[i].w) > obstacle.x
&& obj_rects[i].y < (obstacle.y + obstacle.h)
&& (obj_rects[i].h + obj_rects[i].y) > obstacle.y)
{
// Calculate maximal possible horizontal movement.
if (sign(horizontal_move) == 1)
horizontal_move = obstacle.x - (obj_rects[i].x + obj_rects[i].w);
else if (sign(horizontal_move) == -1)
horizontal_move = (obstacle.x + obstacle.w) - obj_rects[i].x;
}
int obj_new_y = obj_rects[i].y + vertical_move;
// Vertical collision
if (obj_rects[i].x < (obstacle.x + obstacle.w)
&& (obj_rects[i].x + obj_rects[i].w) > obstacle.x
&& obj_new_y < (obstacle.y + obstacle.h)
&& (obj_new_y + obj_rects[i].h) > obstacle.y)
{
if (sign(vertical_move) == 1)
vertical_move = obstacle.y - (obj_rects[i].y + obj_rects[i].h);
else if (sign(vertical_move) == -1)
vertical_move = (obstacle.y + obstacle.h) - obj_rects[i].y;
}
}
}
int cam_velocity = 5;
...
while (!quit) {
...
if (Input[SDL_SCANCODE_RIGHT])
{
x_movement = cam_velocity;
}
else if (Input[SDL_SCANCODE_LEFT])
{
x_movement = -cam_velocity;
}
if (Input[SDL_SCANCODE_UP])
{
y_movement = -cam_velocity;
}
else if (Input[SDL_SCANCODE_DOWN])
{
y_movement = cam_velocity;
}
check_collisions(CAM_RECTS, 3, Box, x_movement, y_movement);
CAMERA_X += x_movement;
CAMERA_Y += y_movement;
for (unsigned int i = 0; i < 3; i++) {
CAM_RECTS[i].x = RECTS[i].x + CAMERA_X;
CAM_RECTS[i].y = RECTS[i].y + CAMERA_Y;
}
...