help with SDL2 mandelbrot code
lazarus / 39-Graphics

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ron77 · 2021-08-25 08:38

hello.

I'm trying to make a Mandelbrot set to display on the window screen
using the SDL2 library in Lazarus. i made a program (console) and
copied a code originally made in C++ and tried to convert it to free
pascal. the code compiles and runs but you get a black screen with
nothing on it... anyone cares to help me find out what I'm doing
wrong? I'm new to Lazarus or free pascal and to use the SDL2 library.

here is the code:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
mandelbrot; {$mode objfpc}{$H+} uses SDL2;  //{$IFDEF UNIX}{$IFDEF
UseCThreads}  //cthreads,  //{$ENDIF}{$ENDIF}  //Classes  //{ you can
add units after this }; var   //window:SDL_Window@   //
Renderer:SDL_Renderer@;   // Event:SDL_Event@;   WIDTH:integer =
1000;   HEIGHT:integer = 1000;    min_num:currency = -2.84; 
 max_num:currency = 1.0;   factor:currency = 1; 
 MAX_ITERATIONS:integer = 200;   x, y, i, n:integer; 
 a,b,ai,bi,a1,b1:currency;    counter, bright,red,green,blue:integer; 
   window: PSDL_Window;     Renderer: PSDL_Renderer; function map(
value, in_min, in_max, out_min, out_max:currency):currency;begin   
map:= (value - in_min) * (out_max - out_min) / (in_max - out_max) +
out_min;end;    procedure main;begin//var//    
SDL_Init(SDL_INIT_EVERYTHING);       // full set up  Window :=
SDL_CreateWindow('Window', 50, 50, 500, 500, SDL_WINDOW_SHOWN);  if
Window = nil then Halt;   Renderer := SDL_CreateRenderer(Window, -1,
0);  if Renderer = nil then Halt;     if
SDL_CreateWindowAndRenderer(1920, 1080, SDL_WINDOW_RESIZABLE, @Window,
@Renderer) <> 0    then Halt;       
SDL_RenderSetLogicalSize(Renderer, WIDTH, HEIGHT);     counter := 0;  
  while True do         max_num -= 0.1 * factor;        min_num +=
0.15 * factor;        factor *= 0.9349;        MAX_ITERATIONS +=
5;           SDL_RenderPresent(Renderer);         for x:= 0 to WIDTH
do            for y := 0 to WIDTH do                    a := map(x, 0,
WIDTH, min_num, max_num);                 b := map(y, 0, WIDTH,
min_num, max_num);                  ai := a;                 bi :=
b;                 n := 0;                   for i := 0 to
MAX_ITERATIONS do                    begin                    a1 := a
* a - b * b;                    b1 := 2 * a * b;                     a
:= a1 + ai;                    b := b1 + bi;                     if
((a + b) > 2) then                        begin                      
break;                        end;                       n := n +1;  
              bright := Trunc(map(n, 0, MAX_ITERATIONS, 0, 255));    
           if ((n = MAX_ITERATIONS)) then                   begin    
             bright := 0;                   end;                   red
:= Trunc(map(bright * bright, 0, 6502, 0, 255));                green
:= bright;                blue := Trunc(map(sqrt(bright), 0,
sqrt(255), 0, 255));                 SDL_SetRenderDrawColor(Renderer,
red, green, blue, 255);                SDL_RenderDrawPoint(Renderer,
x, y);             end;          end;end;  begin main; end.    
here is the original code in C++ that works

Code: C++  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i #include
<iostream> #include <SDL.h>#include <windows.h>#include <math.h> int
WIDTH = 1000;int HEIGHT = 1000; long double min_num = -2.84;long
double max_num = 1.0;long double factor = 1;int MAX_ITERATIONS =
200;   long double map(long double value, long double in_min, long
double in_max, long double out_min, long double out_max){    return
(value - in_min) * (out_max - out_min) / (in_max - out_max) +
out_min;}    int main(int argc, char* argv[]){   
SDL_Init(SDL_INIT_EVERYTHING);     SDL_Window* window;   
SDL_Renderer* Renderer;    SDL_Event Event;     
SDL_CreateWindowAndRenderer(1920, 1080, SDL_WINDOW_RESIZABLE, &window,
&Renderer);    //    int SDL_CreateWindowAndRenderer(1440, 900,
&window, &Renderer);    SDL_RenderSetLogicalSize(Renderer, WIDTH,
HEIGHT);     int counter = 0;     while (1) {         max_num -= 0.1 *
factor;        min_num += 0.15 * factor;        factor *= 0.9349;    
  MAX_ITERATIONS += 5;           SDL_RenderPresent(Renderer);       
//        SDL_RendererPresent(Renderer);        for (int x = 0; x <
WIDTH; x++) {            for (int y = 0; y < WIDTH; y++) {           
    if (SDL_PollEvent(&Event) && Event.type == SDL_QUIT) {           
       return 0;                }                if (GetKeyState('Q')
& 0x8000) {                    return 0;                }            
   long double a = map(x, 0, WIDTH, min_num, max_num);               
long double b = map(y, 0, WIDTH, min_num, max_num);                
long double ai = a;                long double bi = b;               
int n = 0;                   for (int i = 0; i < MAX_ITERATIONS; i++)
{                     long double a1 = a * a - b * b;                
  long double b1 = 2 * a * b;                     a = a1 + ai;       
           b = b1 + bi;                     if ((a + b) > 2) {       
                break;                    }                      
n++;                }                int bright = map(n, 0,
MAX_ITERATIONS, 0, 255);                 if ((n == MAX_ITERATIONS)) { 
                  bright = 0;                 }                  int
red = map(bright * bright, 0, 6502, 0, 255);                int green
= bright;                int blue = map(sqrt(bright), 0, sqrt(255), 0,
255);                 SDL_SetRenderDrawColor(Renderer, red, green,
blue, 255);                SDL_RenderDrawPoint(Renderer, x, y);      
     }          }         counter++;    }       return 0;} 
here is an example of the desired output:

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nouzi · 2021-08-25 10:02

Are you looking for something like this?

https://youtu.be/ARFC6Kf6Tnw

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ron77 · 2021-08-25 10:08

no...
I'm looking for something like this:
https://youtu.be/KnCNfBb2ODQ

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nouzi · 2021-08-25 10:27

See this , It might be a good starting point

https://wiki.freepascal.org/TAChart_Tutorial:_ColorMapSeries,_Zooming