Games101中讲解的光栅化的基础知识,本文就来梳理一下。
在UE中使用UTexture2D可以逐像素绘制纹理:
https://blog.csdn.net/grayrail/article/details/142165442
1.绘制三角形
这里可以通过101中讲解的叉积法逐像素绘制三角形:
绘制效果:
代码如下:
UTexture2D* UMyBlueprintFunctionLibrary::GenTexture(int32 Width, int32 Height)
{// 创建临时纹理UTexture2D* NewTexture = UTexture2D::CreateTransient(Width, Height);// 配置纹理NewTexture->MipGenSettings = TMGS_NoMipmaps;NewTexture->CompressionSettings = TC_VectorDisplacementmap;NewTexture->SRGB = false;// 锁定纹理数据进行写入FTexture2DMipMap& Mip = NewTexture->PlatformData->Mips[0];void* TextureData = Mip.BulkData.Lock(LOCK_READ_WRITE);// 设置默认颜色为黑色FColor* FormattedImageData = static_cast<FColor*>(TextureData);for (int32 y = 0; y < Height; ++y){for (int32 x = 0; x < Width; ++x){FormattedImageData[y * Width + x] = FColor::Black; // 背景颜色设置为黑色}}// 定义三角形顶点(A, B, C)FVector2D A(Width / 2, Height / 4); // 三角形顶点AFVector2D B(Width / 4, 3 * Height / 4); // 三角形顶点BFVector2D C(3 * Width / 4, 3 * Height / 4); // 三角形顶点C// 深红色FColor TriangleColor = FColor(139, 0, 0, 255);// 叉乘判断点P是否在三角形ABC内auto IsPointInTriangle = [](const FVector2D& P, const FVector2D& A, const FVector2D& B, const FVector2D& C) -> bool{FVector2D AP = P - A;FVector2D BP = P - B;FVector2D CP = P - C;FVector2D AB = B - A;FVector2D BC = C - B;FVector2D CA = A - C;// 叉乘结果float Cross1 = AB.X * AP.Y - AB.Y * AP.X; // AB 和 AP 的叉乘float Cross2 = BC.X * BP.Y - BC.Y * BP.X; // BC 和 BP 的叉乘float Cross3 = CA.X * CP.Y - CA.Y * CP.X; // CA 和 CP 的叉乘// 如果三个叉乘结果符号相同,则点在三角形内return (Cross1 >= 0 && Cross2 >= 0 && Cross3 >= 0) || (Cross1 <= 0 && Cross2 <= 0 && Cross3 <= 0);};// 超采样抗锯齿:每个像素划分为2x2子像素int32 SubPixelCount = 4; // 超采样为2x2子像素float InvSubPixelCount = 1.0f / SubPixelCount;// 遍历每个像素并应用抗锯齿逻辑for (int32 y = 0; y < Height; ++y){for (int32 x = 0; x < Width; ++x){int32 CoveredSubPixels = 0;// 遍历2x2子像素for (int32 subY = 0; subY < 2; ++subY){for (int32 subX = 0; subX < 2; ++subX){FVector2D SubPixelPos = FVector2D(x + subX / 2, y + (subY + 0.5f) * 0.5f); // 子像素位置if (IsPointInTriangle(SubPixelPos, A, B, C)){CoveredSubPixels++;}}}// 计算覆盖率并设置像素颜色float Coverage = CoveredSubPixels * InvSubPixelCount; // 覆盖率(0 到 1)if (Coverage > 0){// 根据覆盖率设置颜色,颜色的Alpha通道根据Coverage调整FColor FinalColor = TriangleColor;FinalColor.A = FMath::RoundToInt(255 * Coverage); // 根据覆盖率设置透明度FormattedImageData[y * Width + x] = FinalColor;}}}// 解锁纹理数据Mip.BulkData.Unlock();NewTexture->UpdateResource();return NewTexture;
}
注意:如需了解具体的头文件、Build.cs引用等请看上一篇:https://blog.csdn.net/grayrail/article/details/142165442
2.抗锯齿
绘制好的三角形放大看会有锯齿:
Games101中提到了SSAA(超分辨率抗锯齿/反走样)的方法,来消除锯齿:
大致思路是将一个像素点划分为多个子像素,例如1个像素点细分为4个子像素,然后做叉积包含判断,如果4个像素点有1个包含,覆盖率结果就是0.25,有2个包含结果就是0.5,根据覆盖率的百分比作为插值系数进行绘制,从而得到更好的效果。
UE中绘制效果:
代码如下:
UTexture2D* UMyBlueprintFunctionLibrary::GenTexture(int32 Width, int32 Height)
{// 创建临时纹理UTexture2D* NewTexture = UTexture2D::CreateTransient(Width, Height);// 配置纹理NewTexture->MipGenSettings = TMGS_NoMipmaps;NewTexture->CompressionSettings = TC_VectorDisplacementmap;NewTexture->SRGB = false;// 锁定纹理数据进行写入FTexture2DMipMap& Mip = NewTexture->PlatformData->Mips[0];void* TextureData = Mip.BulkData.Lock(LOCK_READ_WRITE);// 设置默认颜色为黑色FColor* FormattedImageData = static_cast<FColor*>(TextureData);for (int32 y = 0; y < Height; ++y){for (int32 x = 0; x < Width; ++x){FormattedImageData[y * Width + x] = FColor::Black; // 背景颜色设置为黑色}}// 定义三角形顶点(A, B, C)FVector2D A(Width / 2, Height / 4); // 三角形顶点AFVector2D B(Width / 4, 3 * Height / 4); // 三角形顶点BFVector2D C(3 * Width / 4, 3 * Height / 4); // 三角形顶点C// 深红色FColor TriangleColor = FColor(139, 0, 0, 255);// 叉乘判断点P是否在三角形ABC内auto IsPointInTriangle = [](const FVector2D& P, const FVector2D& A, const FVector2D& B, const FVector2D& C) -> bool{FVector2D AP = P - A;FVector2D BP = P - B;FVector2D CP = P - C;FVector2D AB = B - A;FVector2D BC = C - B;FVector2D CA = A - C;// 叉乘结果float Cross1 = AB.X * AP.Y - AB.Y * AP.X; // AB 和 AP 的叉乘float Cross2 = BC.X * BP.Y - BC.Y * BP.X; // BC 和 BP 的叉乘float Cross3 = CA.X * CP.Y - CA.Y * CP.X; // CA 和 CP 的叉乘// 如果三个叉乘结果符号相同,则点在三角形内return (Cross1 >= 0 && Cross2 >= 0 && Cross3 >= 0) || (Cross1 <= 0 && Cross2 <= 0 && Cross3 <= 0);};int SubPixelCount = 8;// 超采样抗锯齿:子像素划分float SubPixelStep = 1.0f / SubPixelCount; // 子像素的步长int32 TotalSubPixels = SubPixelCount * SubPixelCount; // 子像素的总数// 遍历每个像素并应用抗锯齿逻辑for (int32 y = 0; y < Height; ++y){for (int32 x = 0; x < Width; ++x){int32 CoveredSubPixels = 0;// 遍历 SubPixelCount x SubPixelCount 子像素for (int32 subY = 0; subY < SubPixelCount; ++subY){for (int32 subX = 0; subX < SubPixelCount; ++subX){FVector2D SubPixelPos = FVector2D(x + (subX + 0.5f) * SubPixelStep, y + (subY + 0.5f) * SubPixelStep); // 子像素位置if (IsPointInTriangle(SubPixelPos, A, B, C)){CoveredSubPixels++;}}}// 计算覆盖率并设置像素颜色float Coverage = static_cast<float>(CoveredSubPixels) / TotalSubPixels; // 覆盖率(0 到 1)if (Coverage > 0){FColor FinalColor = TriangleColor;FinalColor.R = FMath::RoundToInt(255 * Coverage);FormattedImageData[y * Width + x] = FinalColor;}}}// 解锁纹理数据Mip.BulkData.Unlock();NewTexture->UpdateResource();return NewTexture;
}