How to trace a path with pixels in Raylib? - c++

Question

I am making a double pendulum simulator in Raylib and before I get into the deep physics behind how it works I wanted to finish creating the graphics for it.
So far I created a window, made a double pendulum, and can rotate the pendulums however I want, but as the last thing I need to do before working on the physics is trace its path and I went about it using textures using a RenderTexture2D variable.
However when doing so it does trace the path but only 1/4th of the entire window and I am not sure why.
Most likely it has to do with rltranslatef but I am not sure how to fix it. I have a pendulum.h & .cpp file but they are unrelated to making the graphics for this. Any help is appreciated.
pendulum.h:
#ifndef DOUBLE_PENDULUM_SIM_PENDULUM_H
#define DOUBLE_PENDULUM_SIM_PENDULUM_H
class pendulum {
public:
float pLength{};
float pMass{};
float x{};
float y{};
float pAngle{};
public:
[[nodiscard]] float getX() const ;
[[nodiscard]] float getY() const ;
[[nodiscard]] float getAngle() const ;
void setX(float length, float angle);
void setY(float length, float angle);
void setLength(float length);
void setMass(float mass);
void setAngle(float angle);
pendulum();
pendulum(float length, float mass, float angle) : pLength(length), pMass(mass), pAngle(angle) {}
~pendulum();
};
#endif //DOUBLE_PENDULUM_SIM_PENDULUM_H
pendulum.cpp:
#include "includes/pendulum.h"
#include <cmath>
#include <iostream>
#include <raylib.h>
void pendulum::setX(float length, float angle) {
x = length * sin(angle);
}
void pendulum::setY(float length, float angle) {
y = length * cos(angle);
}
float pendulum::getX() const {
return x;
}
float pendulum::getY() const {
return y;
}
void pendulum::setLength(float length) {
pLength = length;
}
void pendulum::setMass(float mass) {
pMass = mass;
}
float pendulum::getAngle() const {
return pAngle;
}
pendulum::~pendulum() {
std::cout << "\nPendulum destroyed" << std::endl;
}
void pendulum::setAngle(float angle) {
pAngle = angle * DEG2RAD;
}
//Default constructor
pendulum::pendulum() = default;
main.cpp in which the main graphics is drawn:
#include <iostream>
#include "raylib.h"
#include "includes/pendulum.h"
#include <rlgl.h>
#include <cmath>
void _testPendulum();
pendulum pen1;
pendulum pen2;
int main() {
//Prompt to make the initial values themselves
float uLength1, uLength2, uMass1, uMass2, uAngle1, uAngle2;
try {
std::cout << "Please choose the length of each pendulum, starting with Pendulum 1, then Pendulum 2. Each value provided can be up to 7 decimal digits, " << "\n" << "length MUST BE greater than 50 and less than 200" << "\n";
std::cin >> uLength1 >> uLength2;
std::cout << "Please choose the mass of each pendulum, starting with Pendulum 1, then Pendulum 2. Each value provided can be up to 7 decimal digits, " << "\n" << "mass MUST BE greater than 20 and less than 100" << "\n";
std::cin >> uMass1 >> uMass2;
std::cout << "Please choose the starting angle of each pendulum, starting with Pendulum 1, then Pendulum 2. Each value provided can be up to 7 decimal digits" << "\n";
std::cin >> uAngle1 >> uAngle2;
} catch (const std::exception & e) {
std::cout << e.what();
}
//Pendulum 1 settings
pen1.setMass(uMass1);
pen1.setLength(uLength1);
pen1.setAngle(uAngle1);
pen1.setX(pen1.pLength,pen1.getAngle());
pen1.setY(pen1.pLength, pen1.getAngle());
std::cout << "X coord: " << pen1.getX() << " Y coord: " << pen1.getY() << std::endl;
//Pendulum 2 settings
pen2.setMass(uMass2);
pen2.setLength(uLength2);
pen2.setAngle(uAngle2); //Can only set this once and cant anywhere else, why?
pen2.setX( pen2.pLength,pen2.getAngle());
pen2.setY( pen2.pLength,pen2.getAngle());
pen2.x = pen1.getX() + pen2.getX();
pen2.y = pen1.getY() + pen2.getY();
std::cout << "X coord: " << pen2.getX() << " Y coord: " << pen2.getY() << std::endl;
Vector2 origin{0,0};
const double screenWidth = 1440;
const double screenHeight = 1080;
InitWindow((int) screenWidth, (int) screenHeight, "Double-Pendulum-Sim");
int frameCounter = 0;
SetTargetFPS(60);
float px1 = pen1.getX();
float py1 = pen1.getY();
float px2 = pen2.getX();
float py2 = pen2.getY();
RenderTexture2D target = LoadRenderTexture((int) screenWidth, (int) screenHeight);
BeginTextureMode(target);
ClearBackground(RAYWHITE);
EndTextureMode();
while (!WindowShouldClose()) {
Vector2 rod1{px1,py1};
Vector2 rod2 {px2, py2};
/**------------------Update------------------*/
frameCounter++;
uAngle1 += 1.0f;
pen1.setAngle(uAngle1); //Can only set this once and cant anywhere else, why?
pen1.setX(pen1.pLength,pen1.getAngle());
pen1.setY(pen1.pLength, pen1.getAngle());
px1 = pen1.getX();
py1 = pen1.getY();
uAngle2 -= 1.0f;
pen2.setAngle(uAngle2); //Can only set this once and cant anywhere else, why?
pen2.setX( pen2.pLength,pen2.getAngle());
pen2.setY( pen2.pLength,pen2.getAngle());
pen2.x = pen1.getX() + pen2.getX();
pen2.y = pen1.getY() + pen2.getY();
px2 = pen2.getX();
py2 = pen2.getY();
std::cout << frameCounter << std::endl;
/**---------------------------------Draw-Pendulums & Path---------------------------------- */
//TODO: Get pathing to work
BeginDrawing();
BeginTextureMode(target);
DrawPixelV(rod2, RED);
EndTextureMode();
rlTranslatef((float) screenWidth/2,(float) screenHeight/4,0);
DrawTextureRec(target.texture, (Rectangle){0,0, (float) target.texture.width, (float) -target.texture.height}, (Vector2){0,0}, WHITE);
ClearBackground(RAYWHITE);
DrawFPS(-350, -200);
DrawLineEx(origin, rod1, 5.0f, BLACK);
DrawCircle( px1,py1,pen1.pMass,BLACK);
DrawLineEx(rod1, rod2, 5.0f, BLACK);
DrawCircle(px2,py2,pen2.pMass,BLACK);
std::cout << "Pendulum 1 X & Y: " << pen1.getX() << " " << pen1.getY() << std::endl;
std::cout << "Pendulum 2 X & Y: " << pen2.getX() << " " << pen2.getY() << std::endl;
EndDrawing();
}
CloseWindow();
return 0;
}
//Test function
void _testPendulum() {
try {
pen1.setMass(20.0f);
pen1.setLength(150.0f);
pen1.setAngle(0.0f);
pen1.setX(pen1.pLength,pen1.getAngle());
pen1.setY(pen1.pLength, pen1.getAngle());
std::cout << "X coord: " << pen1.getX() << " Y coord: " << pen1.getY() << std::endl;
pen2.setMass(50.0f);
pen2.setLength(150.0f);
pen2.setAngle(0.0f);
pen2.setX( pen2.pLength,pen2.getAngle());
pen2.setY( pen2.pLength,pen2.getAngle());
pen2.x = pen1.getX() + pen2.getX();
pen2.y = pen1.getY() + pen2.getY();
std::cout << "X coord: " << pen2.getX() << " Y coord: " << pen2.getY() << std::endl;
} catch (const std::exception & e) {
std::cout << e.what();
}
}

Answer 1

Your problem comes from DrawPixelV(rod2, RED); which is unable to write where position is negative (try without rlTranslatef to see the idea).
Solution:
Don't use rlTranslatef
Instead make origin, px1, py1, px2 and py2 centered on the screen center (not 0,0).
In main.cpp, I changed these lines and the problem disappeared
Vector2 origin{700,200}; // was origin{0,0};
...
float px1 = pen1.getX() + 700; // +700 was not here
float py1 = pen1.getY() + 200; // +200 was not here
float px2 = pen2.getX() + 700;
float py2 = pen2.getY() + 200;
...
px1 = pen1.getX() + 700;
py1 = pen1.getY() + 200;
...
px2 = pen2.getX() + 700;
py2 = pen2.getY() + 200;