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first example codes: draw julia set
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‎.gitignore

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book
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build
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*.mod

‎sample_codes/README.md

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# 现代Fortran程序设计的随书代码
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## 代码风格
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一般情况下，本书中的Fortran代码将遵守如下代码风格。
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* 对module中的变量与过程通过`private`/`public`对可见性进行限定。
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```fortran
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module m
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implicit none
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private
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public :: a, x
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integer, parameter :: a = 1
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integer, dimension(:), allocatable :: x
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real :: b ! b is private
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end module
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```
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* 用`use`导入module时严格用`only`限定导入内容。
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```fortran
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use m, only: a
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```
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* 用`dimension`属性定义数组。
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* 定义变量时显式写出`len`/`kind`。
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* 命名使用小写字母和下划线。
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* 缩进为四个空格。

‎sample_codes/chapter2/app/main.f90

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program main
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use iso_fortran_env, only: real32
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use julia_set_m, only: generate_julia_set, draw_julia_set
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use save_julia_set_image, only: julia_set_image
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implicit none
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integer, parameter :: width = 80
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integer, parameter :: height = 50
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integer, dimension(height, width) :: julia_set
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complex(real32), parameter :: c = (-0.835, -0.2321)
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call generate_julia_set(julia_set, -1.5, 1.5, -1., 1., c, 1000)
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call draw_julia_set(julia_set)
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call julia_set_image(julia_set)
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end program main

‎sample_codes/chapter2/fpm.toml

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name = "chapter2"
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version = "0.1.0"
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license = "license"
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author = "Jane Doe"
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maintainer = "[email protected]"
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copyright = "Copyright 2021, Jane Doe"
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[build]
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auto-executables = true
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auto-tests = true
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auto-examples = true
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[install]
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library = false

‎sample_codes/chapter2/src/bmp_m.f90

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module bmp_m
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use iso_fortran_env, only: i2 => int16, i4 => int32
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use iso_c_binding, only: c_char
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implicit none
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private
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public :: save_bmp
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integer(kind=i2), parameter :: BMP_HEADER_SIGNATURE = int(z'4D42', i2) ! 'BM' in ASCII
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type :: bmp_file_head
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integer(kind=i4) :: file_size ! size of BMP file, in byte (54 + pixel array)
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integer(kind=i2) :: reserve1 ! not used
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integer(kind=i2) :: reserve2 ! not used
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integer(kind=i4) :: offset_pixel ! starting position of pixel array
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end type
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type :: dib_head
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integer(kind=i4) :: dib_size ! size of DIB, 40 bytes
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integer(kind=i4) :: bmp_width ! image width, in pixel
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integer(kind=i4) :: bmp_height ! image height, in pixel
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integer(kind=i2) :: num_planes
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integer(kind=i2) :: bit_per_pixel ! only 24 is available
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integer(kind=i4) :: compress ! 0, do not compress
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integer(kind=i4) :: image_size ! size of BMP image, in byte
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integer(kind=i4) :: x_ppm ! x pixel per meter
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integer(kind=i4) :: y_ppm ! y pixel per meter
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integer(kind=i4) :: num_colors ! colors in color table
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integer(kind=i4) :: important_color
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end type
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contains
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function save_bmp(image, file_name) result(stat)
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character(kind=c_char), dimension(:,:,:), intent(in) :: image
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character(len=*), intent(in) :: file_name
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logical :: stat
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!===================================================
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type(bmp_file_head) :: header
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type(dib_head) :: dib
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integer(kind=i4) :: row_size
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integer :: unit, ierr, i
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stat = .false.
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if (size(image, dim=1) /= 3) return
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header%offset_pixel = 54
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header%reserve1 = 0
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header%reserve2 = 0
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dib%bit_per_pixel = 24
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dib%bmp_width = size(image, dim=2)
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dib%bmp_height = size(image, dim=3)
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dib%compress = 0
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dib%dib_size = 40
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dib%important_color = 0
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dib%num_colors = 0
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dib%num_planes = 1
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dib%x_ppm = 3780
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dib%y_ppm = 3780
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row_size = ceiling(dib%bit_per_pixel * dib%bmp_width / 32., kind=i4) * 4
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dib%image_size = dib%bmp_height * row_size
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header%file_size = 54 + dib%image_size
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open(newunit=unit, file=file_name, iostat=ierr, access="stream", &
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form="unformatted", action="write", status="unknown")
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if (ierr /= 0) return
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write(unit) BMP_HEADER_SIGNATURE
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write(unit) header
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write(unit) dib
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do i = 0, dib%bmp_height-1
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write(unit, pos=header%offset_pixel+i*row_size+1) image(:,:,i+1)
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end do
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if (mod(dib%bmp_width, 4) /= 0) then
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write(unit, pos=header%offset_pixel+dib%bmp_height*row_size) char(0, c_char)
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end if
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close(unit)
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stat = .true.
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end function save_bmp
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end module bmp_m

‎sample_codes/chapter2/src/julia_set_m.f90

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module julia_set_m
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use iso_fortran_env, only: real32
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implicit none
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private
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public :: generate_julia_set, draw_julia_set
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contains
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function julia_point(z0, c, max_iter) result(n)
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complex(real32), intent(in) :: z0
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complex(real32), intent(in) :: c
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integer, intent(in) :: max_iter
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integer :: n
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! local variables
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complex(real32) :: z
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z = z0
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do n = 1, max_iter
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z = z**2 + c
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if (abs(z) > 2.) exit ! z must diverge when |z| > 2
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end do
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end function julia_point
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subroutine generate_julia_set(set, xmin, xmax, ymin, ymax, c, max_iter)
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integer, dimension(:,:), intent(inout) :: set
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real(real32), intent(in) :: xmin, xmax
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real(real32), intent(in) :: ymin, ymax
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complex(real32), intent(in) :: c
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integer, intent(in) :: max_iter
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! local variables
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integer :: i, j
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real(real32) :: xstep, ystep
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complex(real32) :: z
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xstep = (xmax - xmin) / (size(set, dim=2) - 1)
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ystep = (ymax - ymin) / (size(set, dim=1) - 1)
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do j = 1, size(set, dim=1)
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do i = 1, size(set, dim=2)
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z = complex(xmin + (i - 1) * xstep, ymin + (j - 1) * ystep)
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set(j, i) = julia_point(z, c, max_iter)
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end do
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end do
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end subroutine generate_julia_set
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subroutine draw_julia_set(set)
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integer, dimension(:,:), intent(in) :: set
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! local variables
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character(len=size(set, dim=2)) :: row
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integer :: i, j
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do j = 1, size(set, dim=1)
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do i = 1, size(set, dim=2)
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select case (set(j, i))
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case (1)
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row(i:i) = ' '
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case (2:5)
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row(i:i) = '.'
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case (6:10)
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row(i:i) = ':'
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case (11:15)
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row(i:i) = '*'
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case (16:20)
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row(i:i) = 'x'
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case (21:)
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row(i:i) = '#'
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case default
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write(*, "(a)") "Error: wrong value in set"
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stop
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end select
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end do
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write(*, "(A)") row
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end do
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end subroutine draw_julia_set
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end module julia_set_m

‎sample_codes/chapter2/src/save_julia_set_image.f90

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module save_julia_set_image
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use iso_fortran_env, only: int8
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use iso_c_binding, only: c_char
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use bmp_m, only: save_bmp
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implicit none
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private
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public :: julia_set_image
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contains
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subroutine julia_set_image(set)
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integer, dimension(:,:), intent(in) :: set
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! local variables
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character(kind=c_char), dimension(:,:,:), allocatable :: image
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integer :: pixel
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integer(kind=int8) :: red, green, blue
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integer :: width, height
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integer :: i, j
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height = size(set, dim=1)
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width = size(set, dim=2)
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allocate(image(3,width,height))
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do j = 1, height
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do i = 1, width
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! the pixel order in BMP is from left to right, from bottom to top
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pixel = set(height-j+1,i)
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if (pixel > 1000) then
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red = 0
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green = 0
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blue = 0
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else
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red = int(min(255, pixel*10), kind=int8)
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green = int(min(255, pixel*5), kind=int8)
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blue = int(min(255, pixel*2), kind=int8)
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end if
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image(1,i,j) = char(red, kind=c_char)
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image(2,i,j) = char(green, kind=c_char)
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image(3,i,j) = char(blue, kind=c_char)
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end do
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end do
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if (.not. save_bmp(image, "julia_set.bmp")) write(*,*) "Error saving image"
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end subroutine julia_set_image
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end module save_julia_set_image

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