kolibrios/programs/demos/3DS/FLAT3.INC

draw_triangle:
    ;----------in - eax - x1 shl 16 + y1
    ;------------- -ebx - x2 shl 16 + y2
    ;---------------ecx - x3 shl 16 + y3
    ;---------------edx - color 0x00rrggbb
    ;---------------edi - pointer to screen buffer

	.col equ ebp-4	;dd      ?
	.x1  equ ebp-6	;dw      ?
	.y1  equ  ebp-8  ;dw      ?;+8
	.x2  equ  ebp-10 ;dw      ?
	.y2  equ  ebp-12 ;dw      ?
	.x3  equ  ebp-14  ;dw      ?
	.y3  equ  ebp-16  ;dw      ?;+16
	.dx12 equ  ebp-20  ;  dd      ?
	.dx13 equ  ebp-24  ;  dd      ?;+24
	.dx23 equ  ebp-28  ;  dd      ?

	mov	ebp,esp
      ;  sub     esp,28
	push	edx
    .ch3:
	cmp	ax,bx
	jg	.ch1
    .ch4:			; sort parameters
	cmp	bx,cx
	jg	.ch2
	jle	.chEnd
    .ch1:
	xchg	eax,ebx
	jmp	.ch4
    .ch2:
	xchg	ebx,ecx
	jmp	.ch3
    .chEnd:
     ;   mov     dword[.y1],eax  ; ..and store to user friendly  variables
     ;   mov     dword[.y2],ebx
     ;   mov     dword[.y3],ecx
     ;   mov     [.col],edx
	push	eax
	push	ebx
	push	ecx
	sub	esp,12
	mov	edx,eax 	; eax,ebx,ecx are ORd together into edx which means that
	or	edx,ebx 	; if any *one* of them is negative a sign flag is raised
	or	edx,ecx
	test	edx,80008000h	; Check both X&Y at once
	jne	.end_triangle

	mov	dx,[size_x_var]
	cmp	word[.x1],dx  ;SIZE_X    ; {
	jg	.end_triangle
	cmp	word[.x2],dx  ;SIZE_X     ; This can be optimized with effort
	jg	.end_triangle
	cmp	word[.x3],dx  ;SIZE_X
	jg	.end_triangle	; }

	shr	eax,16
	shr	ebx,16
	shr	ecx,16

	neg	ax		; calculate delta 12
	add	ax,bx
	cwde
	shl	eax,ROUND
	cdq
	mov	bx,[.y2]
	mov	cx,[.y1]
	sub	bx,cx
	;cmp     ebx,0
	jne	.noZero1
	mov	dword[.dx12],0
	jmp	.yesZero1
    .noZero1:
	idiv	ebx
	mov	[.dx12],eax
    .yesZero1:

	mov	ax,[.x3]	; calculate delta 13
	sub	ax,[.x1]
	cwde
	shl	eax,ROUND
	cdq
	mov	bx,[.y3]
	mov	cx,[.y1]
	sub	bx,cx
	;cmp     ebx,0
	jne	.noZero2
	mov	dword[.dx13],0
	jmp	.yesZero2
    .noZero2:
	idiv	ebx
	mov	[.dx13],eax
    .yesZero2:

	mov	ax,[.x3]     ; calculate delta 23 [dx23]
	sub	ax,[.x2]
	cwde
	shl	eax,ROUND
	cdq
	mov	bx,[.y3]
	mov	cx,[.y2]
	sub	bx,cx
	;cmp     ebx,0
	jne	.noZero3
	mov	dword[.dx23],0
	jmp	.yesZero3
    .noZero3:
	idiv	ebx
	mov	[.dx23],eax
    .yesZero3:

	movsx	eax,word[.x1]	; eax - xk1   ;;;
	shl	eax,ROUND
	mov	ebx,eax 	; ebx - xk2   ;;;
	movsx	esi,word[.y1]	; esi - y
    .next_line1:
	mov	ecx,eax 	; ecx - x11
	sar	ecx,ROUND
	mov	edx,ebx 	; edx - x12
	sar	edx,ROUND
	cmp	ecx,edx
	jle	.nochg
	xchg	ecx,edx
    .nochg:
	pusha
	mov	ebx,ecx
	sub	edx,ecx
	mov	ecx,edx
	mov	edx,esi
	mov	eax,[.col]
	call	.horizontal_line
	popa
	add	eax,[.dx13]
	add	ebx,[.dx12]
	inc	esi
	cmp	si,[.y2]
	jl	.next_line1

	movzx	esi,word[.y2]
	movzx	ebx,word[.x2]
	shl	ebx,ROUND
    .next_line2:
	mov	ecx,eax
	sar	ecx,ROUND
	mov	edx,ebx
	sar	edx,ROUND
	cmp	ecx,edx
	jle	.nochg1
	xchg	ecx,edx
    .nochg1:
	pusha
	mov	ebx,ecx
	sub	edx,ecx
	mov	ecx,edx
	mov	edx,esi
	mov	eax,[.col]
	call	.horizontal_line
	popa
	add	eax,[.dx13]
	add	ebx,[.dx23]
	inc	esi
	cmp	si,[.y3]
	jl	.next_line2
    .end_triangle:

       mov     esp,ebp
ret

.horizontal_line:
    ;---------in
    ;---------eax - color of line,  0x00RRGGBB
    ;---------ebx - x1 - x position of line begin
    ;---------ecx - lenght of line
    ;---------edx - y position of line
    ;---------edi - pointer to buffer
	jcxz	.end_hor_l
;        or      edx,edx
;        jl      .end_hor_l
	movzx	esi,word[size_y_var]
	cmp	edx,esi  ;SIZE_Y
	jg	.end_hor_l
	push	eax
	movzx	eax,word[size_x_var]
	lea	eax,[eax*3]
   ;     mov     eax,SIZE_X*3
	mul	edx
	add	edi,eax 	; calculate line begin adress
	;add     edi,ebx
	;shl     ebx,1
	lea	edi,[edi+ebx*2]
	add	edi,ebx
	pop	eax
	cld
	;mov dword[edi-3],0000FF00h
	dec	ecx
	jecxz	.last_pix
    .ddraw:			; Drawing horizontally:
	;push    eax
	stosd			; 4 bytes at a time
	dec edi 		; point to the 4th
	loop	.ddraw
    .last_pix:
	stosw
	shr	eax,16
	stosb
;        mov     byte[edi],0     ; The last 4th will be reset
    .end_hor_l:
ret