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DrawLine 消除 set_pixel

This commit is contained in:
SepComet 2026-06-07 19:25:00 +08:00
parent 08088c8413
commit 16d961e9f3
4 changed files with 205 additions and 105 deletions
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3
docs/CONVENTIONS.md
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@ -100,7 +100,8 @@
这意味着： 这意味着：
- 当前 demo 还没有实现完整的视锥裁剪 - 当前 demo 还没有实现完整的视锥裁剪
- 如果一条线段只有一部分还在屏幕内，但端点已经越出 NDC，整条线仍可能被直接丢弃 - **2D 屏幕空间线段裁剪已实现**：`Rasterizer::DrawLine` 使用 Cohen-Sutherland 算法对屏幕边界做裁剪，部分在屏幕内的线段可以正确绘制，不再整条丢弃
- 3D 视锥裁剪（齐次裁剪空间）仍未实现
## 8. 屏幕与像素坐标 ## 8. 屏幕与像素坐标

1
docs/DEVELOPMENT_GUIDELINES.md
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@ -91,6 +91,7 @@
- 像素写入路径应尽量减少分支和函数调用层级。 - 像素写入路径应尽量减少分支和函数调用层级。
- 像素级写入的 Release 快路径不要使用带额外边界检查的容器访问（例如 `std::vector::at()`）；边界检查应在外层完成。 - 像素级写入的 Release 快路径不要使用带额外边界检查的容器访问（例如 `std::vector::at()`）；边界检查应在外层完成。
- 裁剪、剔除、包围盒收缩要尽早执行，避免把不可见数据送入像素级循环。 - 裁剪、剔除、包围盒收缩要尽早执行，避免把不可见数据送入像素级循环。
- `Rasterizer::DrawLine` 已采用此策略：入口做快速全屏可见性检查，屏幕内直接走 `set_pixel_unsafe` 快路径；屏幕外走 Cohen-Sutherland 裁剪后再走快路径。
- 三角形属性插值、深度测试、纹理采样等未来功能必须先定义定点/整数方案，再接入热路径。 - 三角形属性插值、深度测试、纹理采样等未来功能必须先定义定点/整数方案，再接入热路径。
- PC 调试版可以保留更易读的检查与可视化代码，但 ARM release 路径必须能关闭这些额外成本。 - PC 调试版可以保留更易读的检查与可视化代码，但 ARM release 路径必须能关闭这些额外成本。

301
src/Core/Rasterizer/Rasterizer.cpp
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@ -1,102 +1,199 @@
#include "Rasterizer.h" #include "Rasterizer.h"
#include <Vector2.h> #include <Vector2.h>
#include "Color.h" #include "Color.h"
#include <cmath> #include <cstdint>
#include <cstdint>
namespace Rasterizer
namespace Rasterizer {
{ using namespace Math;
using namespace Math; using namespace RenderData;
using namespace RenderData;
namespace
void Rasterizer::DrawLineHorizontal(const Vector2Int v0, const Vector2Int v1, const Color color) {
{ // Cohen-Sutherland 线段裁剪常量
Vector2Int start = v0, end = v1; const int32_t CS_INSIDE = 0;
if (v0.x > v1.x) const int32_t CS_LEFT = 1;
{ const int32_t CS_RIGHT = 2;
start = v1; const int32_t CS_BOTTOM = 4;
end = v0; const int32_t CS_TOP = 8;
}
inline int32_t cs_compute_outcode(int32_t x, int32_t y, int32_t w, int32_t h)
int32_t dx = end.x - start.x; {
int32_t dy = end.y - start.y; int32_t code = CS_INSIDE;
if (x < 0) code |= CS_LEFT;
int32_t dir = dy < 0 ? -1 : 1; else if (x >= w) code |= CS_RIGHT;
dy *= dir; if (y < 0) code |= CS_TOP;
else if (y >= h) code |= CS_BOTTOM;
if (dx == 0) return; return code;
}
int32_t y = start.y;
int32_t p = 2 * dy - dx; bool cs_clip_line(int32_t& x0, int32_t& y0, int32_t& x1, int32_t& y1,
for (int32_t x = start.x; x <= end.x; x++) int32_t w, int32_t h)
{ {
frameBuffer->set_pixel(x, y, color.to_rgba()); int32_t outcode0 = cs_compute_outcode(x0, y0, w, h);
// 当 p >= 0 时，取上方像素点 int32_t outcode1 = cs_compute_outcode(x1, y1, w, h);
if (p >= 0)
{ while (true)
y += dir; {
p -= 2 * dx; if (!(outcode0 | outcode1))
} {
// 当 p < 0 时，取下方像素点 return true;
p += 2 * dy; }
} if (outcode0 & outcode1)
} {
return false;
void Rasterizer::DrawLineVertical(const Vector2Int v0, const Vector2Int v1, const Color color) }
{
Vector2Int start = v0, end = v1; const int32_t outcode_out = outcode0 ? outcode0 : outcode1;
if (v0.y > v1.y) int32_t x, y;
{
start = v1; if (outcode_out & CS_TOP)
end = v0; {
} x = x0 + (x1 - x0) * (0 - y0) / (y1 - y0);
y = 0;
int32_t dx = end.x - start.x; }
int32_t dy = end.y - start.y; else if (outcode_out & CS_BOTTOM)
{
int32_t dir = dx < 0 ? -1 : 1; x = x0 + (x1 - x0) * (h - 1 - y0) / (y1 - y0);
dx *= dir; y = h - 1;
}
if (dy == 0) return; else if (outcode_out & CS_RIGHT)
{
int32_t x = start.x; y = y0 + (y1 - y0) * (w - 1 - x0) / (x1 - x0);
int32_t p = 2 * dx - dy; x = w - 1;
for (int32_t y = start.y; y <= end.y; y++) }
{ else
frameBuffer->set_pixel(x, y, color.to_rgba()); {
// 当 p >= 0 时，取上方像素点 y = y0 + (y1 - y0) * (0 - x0) / (x1 - x0);
if (p >= 0) x = 0;
{ }
x += dir;
p -= 2 * dy; if (outcode_out == outcode0)
} {
// 当 p < 0 时，取下方像素点 x0 = x; y0 = y;
p += 2 * dx; outcode0 = cs_compute_outcode(x0, y0, w, h);
} }
} else
{
/// <summary> x1 = x; y1 = y;
/// 在给定的起始点和结束点之间绘制一条线段，并使用指定的颜色填充 outcode1 = cs_compute_outcode(x1, y1, w, h);
/// </summary> }
/// <param name="v0">直线顶点 1</param> }
/// <param name="v1">直线顶点 2</param> }
/// <param name="color">绘制的颜色</param> }
/// <remarks>
/// bresenham 画线算法 void Rasterizer::DrawLineHorizontal(Vector2Int v0, Vector2Int v1, uint32_t rgba)
/// </remarks> {
void Rasterizer::DrawLine(const Vector2Int v0, const Vector2Int v1, const Color color) if (v0.x > v1.x)
{ {
int32_t x0 = v0.x, y0 = v0.y; Vector2Int tmp = v0;
int32_t x1 = v1.x, y1 = v1.y; v0 = v1;
v1 = tmp;
if (std::abs(x1 - x0) > std::abs(y1 - y0)) }
{
DrawLineHorizontal(v0, v1, color); const int32_t dx = v1.x - v0.x;
} int32_t dy = v1.y - v0.y;
else if (dx == 0) return;
{
DrawLineVertical(v0, v1, color); const int32_t dir = dy < 0 ? -1 : 1;
} dy *= dir;
}
} const int32_t fb_w = frameBuffer->get_width();
int32_t y = v0.y;
int32_t p = 2 * dy - dx;
for (int32_t x = v0.x; x <= v1.x; ++x)
{
frameBuffer->set_pixel_unsafe(x, y, rgba);
if (p >= 0)
{
y += dir;
p -= 2 * dx;
}
p += 2 * dy;
}
}
void Rasterizer::DrawLineVertical(Vector2Int v0, Vector2Int v1, uint32_t rgba)
{
if (v0.y > v1.y)
{
Vector2Int tmp = v0;
v0 = v1;
v1 = tmp;
}
int32_t dx = v1.x - v0.x;
const int32_t dy = v1.y - v0.y;
if (dy == 0) return;
const int32_t dir = dx < 0 ? -1 : 1;
dx *= dir;
int32_t x = v0.x;
int32_t p = 2 * dx - dy;
for (int32_t y = v0.y; y <= v1.y; ++y)
{
frameBuffer->set_pixel_unsafe(x, y, rgba);
if (p >= 0)
{
x += dir;
p -= 2 * dy;
}
p += 2 * dx;
}
}
void Rasterizer::DrawLineClipped(Vector2Int v0, Vector2Int v1, uint32_t rgba)
{
if (!cs_clip_line(v0.x, v0.y, v1.x, v1.y,
frameBuffer->get_width(), frameBuffer->get_height()))
{
return;
}
const int32_t dx = v1.x - v0.x;
const int32_t dy = v1.y - v0.y;
const int32_t adx = dx < 0 ? -dx : dx;
const int32_t ady = dy < 0 ? -dy : dy;
if (adx > ady)
{
DrawLineHorizontal(v0, v1, rgba);
}
else
{
DrawLineVertical(v0, v1, rgba);
}
}
void Rasterizer::DrawLine(const Vector2Int v0, const Vector2Int v1, const Color color)
{
const int32_t w = frameBuffer->get_width();
const int32_t h = frameBuffer->get_height();
// 快速全屏可见性检查：两点都在屏幕内则跳过裁剪
if (v0.x >= 0 && v0.x < w && v0.y >= 0 && v0.y < h &&
v1.x >= 0 && v1.x < w && v1.y >= 0 && v1.y < h)
{
const uint32_t rgba = color.to_rgba();
const int32_t dx = v1.x - v0.x;
const int32_t dy = v1.y - v0.y;
const int32_t adx = dx < 0 ? -dx : dx;
const int32_t ady = dy < 0 ? -dy : dy;
if (adx > ady)
{
DrawLineHorizontal(v0, v1, rgba);
}
else
{
DrawLineVertical(v0, v1, rgba);
}
return;
}
DrawLineClipped(v0, v1, color.to_rgba());
}
}

5
src/Core/Rasterizer/Rasterizer.h
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@ -12,8 +12,9 @@ namespace Rasterizer
Core::FrameBuffer* frameBuffer; Core::FrameBuffer* frameBuffer;
Core::DepthBuffer* depthBuffer; Core::DepthBuffer* depthBuffer;
void DrawLineHorizontal(const Math::Vector2Int v0, const Math::Vector2Int v1, const RenderData::Color color); void DrawLineHorizontal(Math::Vector2Int v0, Math::Vector2Int v1, uint32_t rgba);
void DrawLineVertical(const Math::Vector2Int v0, const Math::Vector2Int v1, const RenderData::Color color); void DrawLineVertical(Math::Vector2Int v0, Math::Vector2Int v1, uint32_t rgba);
void DrawLineClipped(Math::Vector2Int v0, Math::Vector2Int v1, uint32_t rgba);
public: public:
explicit Rasterizer(Core::FrameBuffer* frameBuffer) :frameBuffer(frameBuffer), depthBuffer(nullptr) {} explicit Rasterizer(Core::FrameBuffer* frameBuffer) :frameBuffer(frameBuffer), depthBuffer(nullptr) {}