LibGDX: 如何使用 OpenGL 2.0 实现平面阴影外观？

Question

所以我试图用 LibGDX 实现 "Polygon Art/Low Poly" 风格。我首先构建一个由三角形组成的模型。

然后使用顶点着色器，我根据高度计算每个顶点的颜色。

问题是，地形是 Gouraud 阴影，而我希望它像这样平坦地着色：

我知道对于更高版本的 OpenGL，glsl 中有一个 "flat" 关键字可以禁用顶点之间的颜色插值。根据我在网上和 post: http://i.stack.imgur.com/DrNx9.jpg 中阅读的内容，我认为我需要让地形中的每个三角形彼此分开？我还需要计算每个三角形的法线？我无法理解其他 Whosebug 中的代码，但这是我尝试做的：

原创

public Model getWorld(){
    returnWorld = new Model();
    modelBuilder = new ModelBuilder();
    modelBuilder.begin();
    worldMeshBuilder = modelBuilder.part("worldPart", GL20.GL_TRIANGLES, Usage.Position | Usage.Normal, new Material());
    pieceMeshBuilder = new MeshBuilder();
    meshPiece = new Mesh(false, 3, 3, 
            new VertexAttribute(Usage.Position, 3, "a_position"), 
            new VertexAttribute(Usage.Normal, 3, "a_normal"), 
            new VertexAttribute(Usage.ColorPacked, 4, "a_color"));
    Vector3 vectorCopy = new Vector3();
    for(int i = 0; i < world.length - 1; i++){
        for(int j = 0; j < world[0].length - 1; j++){
            if((i + j) % 2 == 0){
                pieceMeshBuilder.begin(Usage.Position | Usage.Normal, renderType);
                pieceMeshBuilder.triangle(
                    vectorCopy = verticies[i][j],
                    vectorCopy = verticies[i][j + 1],
                    vectorCopy = verticies[i + 1][j + 1]
                );
                worldMeshBuilder.addMesh(pieceMeshBuilder.end());
                pieceMeshBuilder.begin(Usage.Position | Usage.Normal, renderType);
                pieceMeshBuilder.triangle(
                        vectorCopy = verticies[i + 1][j + 1],
                        vectorCopy = verticies[i + 1][j],
                        vectorCopy = verticies[i][j]
                );
                worldMeshBuilder.addMesh(pieceMeshBuilder.end());
            } else {
                pieceMeshBuilder.begin(Usage.Position | Usage.Normal, renderType);
                pieceMeshBuilder.triangle(
                    vectorCopy = verticies[i][j],
                    vectorCopy = verticies[i][j + 1],
                    vectorCopy = verticies[i + 1][j]
                );
                worldMeshBuilder.addMesh(pieceMeshBuilder.end());
                pieceMeshBuilder.begin(Usage.Position | Usage.Normal, renderType);
                pieceMeshBuilder.triangle(
                        vectorCopy = verticies[i + 1][j + 1],
                        vectorCopy = verticies[i + 1][j],
                        vectorCopy = verticies[i][j + 1]
                );
                worldMeshBuilder.addMesh(pieceMeshBuilder.end());
            }
        }
    }
    returnWorld = modelBuilder.end();
    return returnWorld;
}

现在：

public Model getWorld(){
    returnWorld = new Model();
    modelBuilder = new ModelBuilder();
    modelBuilder.begin();
    worldMeshBuilder = modelBuilder.part("worldPart", GL20.GL_LINES, Usage.Position | Usage.Normal, new Material());

    for(int i = 0; i < world.length - 1; i++){
        for(int j = 0; j < world[0].length - 1; j++){

            Vector3 normal1 = calcNormal(verticies[i][j], verticies[i + 1][j], verticies[i + 1][j + 1]);
            Vector3 normal2 = calcNormal(verticies[i][j], verticies[i + 1][j + 1], verticies[i][j + 1]);

            if((i + j) % 2 == 0){
                meshPiece = new Mesh(false, 18, 3, 
                        new VertexAttribute(Usage.Position, 3, "a_position"), 
                        new VertexAttribute(Usage.Normal, 3, "a_normal")//, 
                        //new VertexAttribute(Usage.ColorPacked, 4, "a_color")
                        );
                worldMeshBuilder.addMesh(meshPiece.setVertices(new float[] {
                        verticies[i][j].x, verticies[i][j].y, verticies[i][j].z, normal1.x, normal1.y, normal1.z,
                        verticies[i + 1][j].x, verticies[i + 1][j].y, verticies[i + 1][j].z, normal1.x, normal1.y, normal1.z, 
                        verticies[i + 1][j + 1].x, verticies[i + 1][j + 1].y, verticies[i + 1][j + 1].z, normal1.x, normal1.y, normal1.z,
                    }));
                meshPiece = new Mesh(false, 18, 3, 
                        new VertexAttribute(Usage.Position, 3, "a_position"), 
                        new VertexAttribute(Usage.Normal, 3, "a_normal")//, 
                        //new VertexAttribute(Usage.ColorPacked, 4, "a_color")
                        );
                worldMeshBuilder.addMesh(meshPiece.setVertices(new float[] {
                        verticies[i][j].x, verticies[i][j].y, verticies[i][j].z, normal2.x, normal2.y, normal2.z,
                        verticies[i + 1][j + 1].x, verticies[i + 1][j + 1].y, verticies[i + 1][j + 1].z, normal2.x, normal2.y, normal2.z, 
                        verticies[i][j + 1].x, verticies[i][j + 1].y, verticies[i][j + 1].z, normal2.x, normal2.y, normal2.z,
                    }));
            } else {
                meshPiece = new Mesh(false, 18, 3, 
                        new VertexAttribute(Usage.Position, 3, "a_position"), 
                        new VertexAttribute(Usage.Normal, 3, "a_normal")//, 
                        //new VertexAttribute(Usage.ColorPacked, 4, "a_color")
                        );
                worldMeshBuilder.addMesh(meshPiece.setVertices(new float[] {
                        verticies[i][j].x, verticies[i][j].y, verticies[i][j].z, normal1.x, normal1.y, normal1.z,
                        verticies[i + 1][j].x, verticies[i + 1][j].y, verticies[i + 1][j].z, normal1.x, normal1.y, normal1.z, 
                        verticies[i][j + 1].x, verticies[i][j + 1].y, verticies[i][j + 1].z, normal1.x, normal1.y, normal1.z,
                    }));
                meshPiece = new Mesh(false, 18, 3, 
                        new VertexAttribute(Usage.Position, 3, "a_position"), 
                        new VertexAttribute(Usage.Normal, 3, "a_normal")//, 
                        //new VertexAttribute(Usage.ColorPacked, 4, "a_color")
                        );
                worldMeshBuilder.addMesh(meshPiece.setVertices(new float[] {
                        verticies[i + 1][j].x, verticies[i + 1][j].y, verticies[i + 1][j].z, normal2.x, normal2.y, normal2.z,
                        verticies[i + 1][j + 1].x, verticies[i + 1][j + 1].y, verticies[i + 1][j + 1].z, normal2.x, normal2.y, normal2.z, 
                        verticies[i][j + 1].x, verticies[i][j + 1].y, verticies[i][j + 1].z, normal2.x, normal2.y, normal2.z,
                    }));
            }
        }
    }
    returnWorld = modelBuilder.end();
    return returnWorld;
}

问题是新代码没有渲染任何东西...我查看了 ModelBuilder、MeshBuilder、Mesh 和 VertexAttribute/s 的 API，但我不明白为什么会这样不工作。任何帮助都会很棒，因为这是非常令人沮丧的一天。非常感谢！

Answer 1

平坦平滑的着色通常由顶点法线和颜色在整个面上的插值方式决定。

通常在平滑模型中，每个顶点的法线针对同一位置的每个面点进行平均。每个共享顶点位置的法线对于每个面都是相同的。这就是使照明平滑的原因，因为边缘没有突然变化。

在平面着色模型中，顶点法线与相邻面不匹配，而是每个顶点法线与面法线相同。这会导致边缘处的法线值发生突然变化。

这通常可以在您使用的任何 3D 建模包中进行修改，或者如果地形是程序生成的，则可以通过稍微修改您的法线生成代码来进行修改。

下图显示了平坦法线和平滑法线的区别。较深的蓝色线条代表平均平滑法线，较浅（青色）线条代表粗糙的面部法线。

您应该能够在一次绘制调用中将所有三角形绘制在一起。您不需要分割网格。

LibGDX: 如何使用 OpenGL 2.0 实现平面阴影外观？

LibGDX: How can I achieve a flat shaded look with OpenGL 2.0?

java

opengl

libgdx

glsl

opengl-2.0