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adjust for clearity
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skywind3000 committed Aug 12, 2015
1 parent 25704fd commit 1abb5fe
Showing 1 changed file with 93 additions and 110 deletions.
203 changes: 93 additions & 110 deletions mini3d.c
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@
// 2007.7.02 skywind implementate texture and color render
// 2008.3.15 skywind fixed a trapezoid issue
// 2015.8.09 skywind rewrite with more comment
// 2015.8.12 skywind adjust interfaces for clearity
//
//=====================================================================
#include <stdio.h>
Expand Down Expand Up @@ -308,6 +309,7 @@ typedef struct { vertex_t v, v1, v2; } edge_t;
typedef struct { float top, bottom; edge_t left, right; } trapezoid_t;
typedef struct { vertex_t v, step; int x, y, w; } scanline_t;


void vertex_rhw_init(vertex_t *v) {
float rhw = 1.0f / v->pos.w;
v->rhw = rhw;
Expand Down Expand Up @@ -355,94 +357,90 @@ void vertex_add(vertex_t *y, const vertex_t *x) {
y->color.b += x->color.b;
}

// 1
// 2 3
void trapezoid_init_edge_up(trapezoid_t *trape,
const vertex_t *v1, const vertex_t *v2, const vertex_t *v3) {
const vertex_t *v;
if (v2->pos.x > v3->pos.x) v = v2, v2 = v3, v3 = v;
trape->top = v1->pos.y;
trape->bottom = v2->pos.y;
trape->left.v = *v1;
trape->right.v = *v1;
trape->left.v1 = *v1;
trape->left.v2 = *v2;
trape->right.v1 = *v1;
trape->right.v2 = *v3;
}

// 1 2
// 3
void trapezoid_init_edge_down(trapezoid_t *trape,
const vertex_t *v1, const vertex_t *v2, const vertex_t *v3) {
const vertex_t *v;
if (v1->pos.x > v2->pos.x) v = v1, v1 = v2, v2 = v;
trape->top = v1->pos.y;
trape->bottom = v3->pos.y;
trape->left.v = *v1;
trape->right.v = *v2;
trape->left.v1 = *v1;
trape->left.v2 = *v3;
trape->right.v1 = *v2;
trape->right.v2 = *v3;
}

// 1 1
// 2 or 2
// (t) 3 3 (t)
void trapezoid_init_edges(trapezoid_t *up, trapezoid_t *down,
const vertex_t *v1, const vertex_t *v2, const vertex_t *v3) {
float f = (v3->pos.y - v1->pos.y) / (v2->pos.y - v1->pos.y);
vertex_t t1 = *v1;
vertex_t t2 = *v2;
vertex_t t3 = *v3;
vertex_t t;

up->top = t1.pos.y;
up->bottom = t2.pos.y;
down->top = t2.pos.y;
down->bottom = t3.pos.y;

vertex_interp(&t, &t1, &t2, f);

if (t.pos.x <= t3.pos.x) {
up->left.v1 = t1;
up->left.v2 = t2;
up->right.v1 = t1;
up->right.v2 = t3;
down->left.v1 = t2;
down->left.v2 = t3;
down->right.v1 = t1;
down->right.v2 = t3;
} else {
up->left.v1 = t1;
up->left.v2 = t3;
up->right.v1 = t1;
up->right.v2 = t2;
down->left.v1 = t1;
down->left.v2 = t3;
down->right.v1 = t2;
down->right.v2 = t3;
// 根据三角形生成 0-2 个梯形，并且返回合法梯形的数量
int trapezoid_init_triangle(trapezoid_t *trap, const vertex_t *p1,
const vertex_t *p2, const vertex_t *p3) {
const vertex_t *p;
float k, x;

if (p1->pos.y > p2->pos.y) p = p1, p1 = p2, p2 = p;
if (p1->pos.y > p3->pos.y) p = p1, p1 = p3, p3 = p;
if (p2->pos.y > p3->pos.y) p = p2, p2 = p3, p3 = p;
if (p1->pos.y == p2->pos.y && p1->pos.y == p3->pos.y) return 0;
if (p1->pos.x == p2->pos.x && p1->pos.x == p3->pos.x) return 0;

if (p1->pos.y == p2->pos.y) { // triangle down
if (p1->pos.x > p2->pos.x) p = p1, p1 = p2, p2 = p;
trap[0].top = p1->pos.y;
trap[0].bottom = p3->pos.y;
trap[0].left.v1 = *p1;
trap[0].left.v2 = *p3;
trap[0].right.v1 = *p2;
trap[0].right.v2 = *p3;
return (trap[0].top < trap[0].bottom)? 1 : 0;
}

if (p2->pos.y == p3->pos.y) { // triangle up
if (p2->pos.x > p3->pos.x) p = p2, p2 = p3, p3 = p;
trap[0].top = p1->pos.y;
trap[0].bottom = p3->pos.y;
trap[0].left.v1 = *p1;
trap[0].left.v2 = *p2;
trap[0].right.v1 = *p1;
trap[0].right.v2 = *p3;
return (trap[0].top < trap[0].bottom)? 1 : 0;
}

trap[0].top = p1->pos.y;
trap[0].bottom = p2->pos.y;
trap[1].top = p2->pos.y;
trap[1].bottom = p3->pos.y;

k = (p3->pos.y - p1->pos.y) / (p2->pos.y - p1->pos.y);
x = p1->pos.x + (p2->pos.x - p1->pos.x) * k;

if (x <= p3->pos.x) { // triangle left
trap[0].left.v1 = *p1;
trap[0].left.v2 = *p2;
trap[0].right.v1 = *p1;
trap[0].right.v2 = *p3;
trap[1].left.v1 = *p2;
trap[1].left.v2 = *p3;
trap[1].right.v1 = *p1;
trap[1].right.v2 = *p3;
} else { // triangle right
trap[0].left.v1 = *p1;
trap[0].left.v2 = *p3;
trap[0].right.v1 = *p1;
trap[0].right.v2 = *p2;
trap[1].left.v1 = *p1;
trap[1].left.v2 = *p3;
trap[1].right.v1 = *p2;
trap[1].right.v2 = *p3;
}

return 2;
}

void trapezoid_edge_interp(trapezoid_t *trape, float y) {
float s1 = trape->left.v2.pos.y - trape->left.v1.pos.y;
float s2 = trape->right.v2.pos.y - trape->right.v1.pos.y;
float t1 = (y - trape->left.v1.pos.y) / s1;
float t2 = (y - trape->right.v1.pos.y) / s2;
vertex_interp(&trape->left.v, &trape->left.v1, &trape->left.v2, t1);
vertex_interp(&trape->right.v, &trape->right.v1, &trape->right.v2, t2);
// 按照 Y 坐标计算出左右两条边纵坐标等于 Y 的顶点
void trapezoid_edge_interp(trapezoid_t *trap, float y) {
float s1 = trap->left.v2.pos.y - trap->left.v1.pos.y;
float s2 = trap->right.v2.pos.y - trap->right.v1.pos.y;
float t1 = (y - trap->left.v1.pos.y) / s1;
float t2 = (y - trap->right.v1.pos.y) / s2;
vertex_interp(&trap->left.v, &trap->left.v1, &trap->left.v2, t1);
vertex_interp(&trap->right.v, &trap->right.v1, &trap->right.v2, t2);
}

void trapezoid_init_scan_line(const trapezoid_t *trape, scanline_t *scanline, int y) {
float width = trape->right.v.pos.x - trape->left.v.pos.x;
scanline->x = (int)(trape->left.v.pos.x + 0.5f);
scanline->w = (int)(trape->right.v.pos.x + 0.5f) - scanline->x;
// 根据左右两边的端点，初始化计算出扫描线的起点和步长
void trapezoid_init_scan_line(const trapezoid_t *trap, scanline_t *scanline, int y) {
float width = trap->right.v.pos.x - trap->left.v.pos.x;
scanline->x = (int)(trap->left.v.pos.x + 0.5f);
scanline->w = (int)(trap->right.v.pos.x + 0.5f) - scanline->x;
scanline->y = y;
scanline->v = trape->left.v;
if (trape->left.v.pos.x >= trape->right.v.pos.x) scanline->w = 0;
vertex_division(&scanline->step, &trape->left.v, &trape->right.v, width);
scanline->v = trap->left.v;
if (trap->left.v.pos.x >= trap->right.v.pos.x) scanline->w = 0;
vertex_division(&scanline->step, &trap->left.v, &trap->right.v, width);
}


Expand Down Expand Up @@ -650,15 +648,15 @@ void device_draw_scanline(device_t *device, scanline_t *scanline) {
}

// 主渲染函数
void device_render_trape(device_t *device, trapezoid_t *trape) {
void device_render_trap(device_t *device, trapezoid_t *trap) {
scanline_t scanline;
int j, top, bottom;
top = (int)(trape->top + 0.5f);
bottom = (int)(trape->bottom + 0.5f);
top = (int)(trap->top + 0.5f);
bottom = (int)(trap->bottom + 0.5f);
for (j = top; j < bottom; j++) {
if (j >= 0 && j < device->height) {
trapezoid_edge_interp(trape, (float)j + 0.5f);
trapezoid_init_scan_line(trape, &scanline, j);
trapezoid_edge_interp(trap, (float)j + 0.5f);
trapezoid_init_scan_line(trap, &scanline, j);
device_draw_scanline(device, &scanline);
}
if (j >= device->height) break;
Expand Down Expand Up @@ -689,8 +687,10 @@ void device_draw_primitive(device_t *device, const vertex_t *v1,

// 纹理或者色彩绘制
if (render_state & (RENDER_STATE_TEXTURE | RENDER_STATE_COLOR)) {
trapezoid_t trape1, trape2;
vertex_t t1 = *v1, t2 = *v2, t3 = *v3, t;
vertex_t t1 = *v1, t2 = *v2, t3 = *v3;
trapezoid_t traps[2];
int n;

t1.pos = p1;
t2.pos = p2;
t3.pos = p3;
Expand All @@ -701,29 +701,12 @@ void device_draw_primitive(device_t *device, const vertex_t *v1,
vertex_rhw_init(&t1); // 初始化 w
vertex_rhw_init(&t2); // 初始化 w
vertex_rhw_init(&t3); // 初始化 w

// 三角形排序，从上到下 t1, t2, t3
if (t1.pos.y > t2.pos.y) t = t1, t1 = t2, t2 = t;
if (t1.pos.y > t3.pos.y) t = t1, t1 = t3, t3 = t;
if (t2.pos.y > t3.pos.y) t = t2, t2 = t3, t3 = t;

if (t1.pos.y == t2.pos.y && t1.pos.y == t3.pos.y) { // 调过 0高度
return;
}
// 拆分三角形为0-2个梯形，并且返回可用梯形数量
n = trapezoid_init_triangle(traps, &t1, &t2, &t3);

if (t1.pos.y == t2.pos.y) { // t1 在上，t2, t3 在一条水平线上
trapezoid_init_edge_down(&trape1, &t1, &t2, &t3);
device_render_trape(device, &trape1); // 渲染梯形
}
else if (t2.pos.y == t3.pos.y) { // t1, t2同水平线，t3在下
trapezoid_init_edge_up(&trape2, &t1, &t2, &t3);
device_render_trape(device, &trape2); // 渲染梯形
}
else { // t1上，t2中，t3下，计算一个中点 t 使得分成上下两三角形
trapezoid_init_edges(&trape1, &trape2, &t1, &t2, &t3);
device_render_trape(device, &trape1); // 渲染上部分梯形
device_render_trape(device, &trape2); // 渲染下部分梯形
}
if (n >= 1) device_render_trap(device, &traps[0]);
if (n >= 2) device_render_trap(device, &traps[1]);
}

if (render_state & RENDER_STATE_WIREFRAME) { // 线框绘制
Expand Down

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