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70a2b11271
* demo of prog8 recursion to draw a fractal tree * feat: comments * fix: comment formatting * feat: make minimum branch size a tunable parameter
80 lines
2.5 KiB
Lua
80 lines
2.5 KiB
Lua
; Draw a fractal tree recursively
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; This is an example of doing recursion with local per-call state that has to
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; be preserved across recursive calls, as opposed to queens.p8 where the
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; recursive function only modifies global state.
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;
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; Note: this program can be compiled for multiple target systems.
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%import floats
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%import graphics
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%zeropage basicsafe
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main {
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; Adjust these parameters to change the appearance of the tree:
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; 1. the angle of each branch away from its parent (left and right)
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const float delta_theta = floats.π / 6
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; 2. the size of each branch relative to its parent
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const float shrink_factor = 2.0 / 3.0
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; 3. the size of the smallest branch (in pixels)
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const float minimum_branch = 1.0
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; These stacks hold copies of the parameters during recursive calls
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uword[11] x
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ubyte[11] y
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float[11] theta
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float[11] length
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; This points to the current level of stack in use
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ubyte stack_pointer
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; draw a branch starting at (x1, y1) at angle th1 with length len1
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; recurses if length is large enough
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sub draw_branch(uword x1, ubyte y1, float th1, float len1) {
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uword x2 = (x1 as float + len1 * floats.cos(th1)) as uword
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ubyte y2 = (y1 as float - len1 * floats.sin(th1)) as ubyte
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graphics.line(x1, y1, x2, y2)
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if len1 >= minimum_branch {
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; push parameters onto stacks
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x[stack_pointer] = x1
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y[stack_pointer] = y1
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theta[stack_pointer] = th1
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length[stack_pointer] = len1
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stack_pointer += 1
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draw_branch(x2, y2, th1 - delta_theta, len1 * shrink_factor)
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; recover parameters after recursive call
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x1 = x[stack_pointer - 1]
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y1 = y[stack_pointer - 1]
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th1 = theta[stack_pointer - 1]
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len1 = length[stack_pointer - 1]
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x2 = (x1 as float + len1 * floats.cos(th1)) as uword
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y2 = (y1 as float - len1 * floats.sin(th1)) as ubyte
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draw_branch(x2, y2, th1 + delta_theta, len1 * shrink_factor)
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; pop stack level
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stack_pointer -= 1
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}
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}
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sub start() {
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graphics.enable_bitmap_mode()
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draw_branch(graphics.WIDTH / 2, graphics.HEIGHT - 1,
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floats.π / 2,
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graphics.HEIGHT / 2 * shrink_factor)
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; done rendering; wait for a key before exiting
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do {
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ubyte key = cbm.GETIN2()
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} until key != 0
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graphics.disable_bitmap_mode()
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}
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}
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