format ELF64

initial_width = 800
initial_height = 450

FLAG_MSAA_4X_HINT = 32

struc splat x {
	dd x, x, x, x
}

struc Vec2 x,y {
	dd x, y, 0.0, 0.0
}

struc Ball x, y, r {
	.pos Vec2 x, y
	.vel splat 0.0
	.rad splat r
}

public _start

extrn SetConfigFlags
extrn InitWindow
extrn SetTargetFPS
extrn WindowShouldClose
extrn GetMouseWheelMove
extrn IsMouseButtonDown
extrn GetMousePosition
extrn GetScreenWidth
extrn GetScreenHeight
extrn BeginDrawing
extrn EndDrawing
extrn ClearBackground
extrn DrawCircleV
extrn _exit

section '.text' executable

_start:
	; enable anti-aliasing
	mov edi, FLAG_MSAA_4X_HINT
	call SetConfigFlags

	; initialise window
	mov edi, initial_width
	mov esi, initial_height
	mov rdx, title
	call InitWindow

	; 60 fps
	mov edi, 60
	call SetTargetFPS

	jmp loop_entr

main_loop:
	; change ball size
	call GetMouseWheelMove
	shufps xmm0, xmm0, 0x0
	addps xmm0, [ball.rad]
	maxps xmm0, [minimum_radius]
	movlps [ball.rad], xmm0

	; check if lmb is pressed
	xor edi, edi
	call IsMouseButtonDown
	test eax, eax
	jz no_click

	; accelerate ball towards mouse
	call GetMousePosition
	subps xmm0, [ball.pos]
	mulps xmm0, [mouse_seek_speed]

	jmp move_and_draw

no_click:
	; get width/height
	call GetScreenWidth
	mov ebx, eax
	call GetScreenHeight

	; convert width/height to packed single precision floats
	cvtsi2ss xmm0, ebx
	cvtsi2ss xmm1, eax
	movlhps xmm0, xmm1
	shufps xmm0, xmm0, 0x8

	; load ball position and radius
	movlps xmm1, [ball.pos]
	movlps xmm2, [ball.rad]

	; calculate upper boundaries
	subps xmm0, xmm2

	; stash boundaries for later
	movaps xmm3, xmm2
	movaps xmm4, xmm0

	; dirty, rotten, low-down, no-good hack
	cmpnleps xmm2, xmm1                 ; out of left/top bounds mask
	cmpltps xmm0, xmm1                  ; out of right/bottom bounds mask
	orps xmm0, xmm2                     ; or the masks
	andps xmm0, [restitution_minus_one] ; mask & restitution coefficient minus one
	addps xmm0, [ones]                  ; add ones to create bounce vector (0.0 -> 1.0, restitution - 1.0 -> restitution)
	maxps xmm1, xmm3
	minps xmm1, xmm4                    ; keep position in bounds

	; scale velocity by bounce vector
	mulps xmm0, [ball.vel]

	; apply air resistance and gravity
	mulps xmm0, [air_resistance_coef]
	addps xmm0, [grav_accel]

	; store position
	movlps [ball.pos], xmm1

move_and_draw:
	; store velocity
	movlps [ball.vel], xmm0

	; move ball
	addps xmm0, [ball.pos]
	movlps [ball.pos], xmm0

	; draw frame
	call BeginDrawing

	; black background
	xor edi, edi
	call ClearBackground

	; sphere
	movlps xmm0, [ball.pos]
	movss xmm1, [ball.rad]
	mov rdi, 0xFF2C7500 ; green
	call DrawCircleV

	call EndDrawing

loop_entr:
	call WindowShouldClose
	test eax, eax
	jz main_loop

	xor edi, edi
	call _exit

section '.data' writable align 16
	mouse_seek_speed      splat 0.5
	minimum_radius        splat 2.5
	air_resistance_coef   splat 0.99
	restitution_minus_one splat -1.8
	ones                  splat 1.0

	grav_accel Vec2 0.0, 0.69

	ball Ball 400.0, 250.0, 25.0

	title db 'ball simulator',0