Mandelbrot demo: show the image

[certik]

TODO:

• Get the image out of Fortran and into JavaScript using the approach described at: https://gitlab.com/lfortran/lfortran/-/issues/761#note_1056724358
• Show the image on a canvas from JavaScript

Old:

Here is a code that compiles to WAT at dev.lfortran.org: https://gitlab.com/lfortran/lfortran/-/issues/702#note_1059822597, but the execution window says:

ERROR: The code could not be executed. Either there is a runtime error or there is an issue at our end.

So we need to investigate what is going on.

[certik]

I had to reduce the image size. This works:

program mandelbrot
    implicit none
    integer  , parameter :: rk       =  8
    integer  , parameter :: i_max    =  80
    integer  , parameter :: j_max    =  60
    integer  , parameter :: n_max    =  100
    real (rk), parameter :: x_centre = -0.5_rk
    real (rk), parameter :: y_centre =  0.0_rk
    real (rk), parameter :: width    =  4.0_rk
    real (rk), parameter :: height   =  3.0_rk
    real (rk), parameter :: dx_di    =   width / i_max
    real (rk), parameter :: dy_dj    = -height / j_max
    real (rk), parameter :: x_offset = x_centre - 0.5_rk * (i_max + 1) * dx_di
    real (rk), parameter :: y_offset = y_centre - 0.5_rk * (j_max + 1) * dy_dj
    integer :: image(i_max, j_max)
    integer   :: i
    integer   :: j
    integer   :: n
    real (rk) :: x
    real (rk) :: y
    real (rk) :: x_0
    real (rk) :: y_0
    real (rk) :: x_sqr
    real (rk) :: y_sqr

    do j = 1, j_max
      y_0 = y_offset + dy_dj * j
      do i = 1, i_max
        x_0 = x_offset + dx_di * i
        x = 0.0_rk
        y = 0.0_rk
        n = 0
        do
          x_sqr = x * x
          y_sqr = y * y
          if (x_sqr + y_sqr > 4.0_rk) then
            image(i,j) = 255
            exit
          end if
          if (n == n_max) then
            image(i,j) = 0
            exit
          end if
          y = y_0 + 2.0_rk * x * y
          x = x_0 + x_sqr - y_sqr
          n = n + 1
        end do
      end do
    end do

    print '(a)', 'P2'
    print '(i0, 1x, i0)', i_max, j_max
    print '(i0)', 255
    do j = 1, j_max
      do i = 1, i_max
        print '(i0)', image(i,j)
      end do
    end do
end program mandelbrot

And produces the correct output. Just copy & paste the output into a file mandelbrot.pbm and open it in some image program and it works!

[certik]

The last missing piece is how to show the image in the webpage itself as an image. The approach how to do it is described here:

• https://gitlab.com/lfortran/lfortran/-/issues/761#note_1056724358

[Shaikh-Ubaid]

It seems the initial example code failed due to insufficient memory. We recently increased the memory limit in lfortran/lfortran#126. Probably, the current lfortran.wasm at dev.lfortran.org was compiled prior to the increase in memory and I guess, therefore the error. I will update the lfortran.wasm (and lfortran.js) at dev.lfortran.org with the latest one soon.

[certik]

@Shaikh-Ubaid I think that's right. Even the pow that we fixed didn't work, so you can see I worked around it too. These are both quite easy to fix.

[Shaikh-Ubaid]

Please, could someone possibly share if this issue is complete?

[certik]

This is fixed! Thank you so much @Shaikh-Ubaid for implementing it. Here is how it looks like for me now at dev.lfortran.org: