我正在尝试使用单独的“顶点数组”对象渲染两个三角形。我在C＃上使用OpenTK（与定义的OpenGL API相比，它提供几乎相同的API）。这是我的代码：
我从声明变量开始。
public partial class Form1 : Form
{
public Form1() {
InitializeComponent();
}
bool loaded = false; //do not use glcontrol before it is not loaded
private uint VAO1;
private uint object1_vertex_buffer; private uint object1_vertices_size; private uint object1_index_buffer;
private uint object2_vertex_buffer; private uint object2_vertices_size; private uint object2_index_buffer;
private uint VAO2;
private uint VBO;
int VertexShader;
int FragmentShader;
int ShaderProgram;
private float[] object1_vertices = new float[] {
-0.2f, 0.0f, 0.0f,
0.2f, 0.0f, 0.0f,
0.0f, 0.2f, 0.0f
};
private float[] object2_vertices = new float[] {
-0.5f, 0.0f, 0.0f,
0.5f, 0.0f, 0.0f,
0.0f, 0.4f, 0.0f
};
private int[] object1_indices = new int[] { 0, 1, 2 };
private int[] object2_indices = new int[] { 0, 1, 2 };
我在这里画每一帧：
private void glControl1_Paint(object sender, PaintEventArgs e)
{
if (!loaded)//<--------------------------------------
return;//<--------------------------------------
// Clear the color buffer.
GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
GL.UseProgram(ShaderProgram);
// Object 1
GL.BindVertexArray(VAO1);
// drawelements requires count of elements, not bytes
GL.DrawElements(PrimitiveType.Triangles, object1_indices.Length, DrawElementsType.UnsignedInt, 0);
// Object 2
GL.BindVertexArray(VAO2);
GL.DrawElements(PrimitiveType.Triangles, object2_indices.Length, DrawElementsType.UnsignedInt, 0);
ErrorCode miauw = GL.GetError(); /// AND I GET HERE NO ERROR!
/// at the end I have a screen filled by a background color, which is set in GL.ClearColor()
glControl1.SwapBuffers();
}
在这里，我对OpenGL数组和缓冲区进行了初始化。我在这里初始化两个顶点数组对象（每个三角形一个）和两个缓冲区（每个三角形）：顶点和索引。我为他们设置了适当的字节长度
private void glControl1_Load(object sender, EventArgs e) {
loaded = true;
GL.ClearColor(Color.SkyBlue);
GL.Enable(EnableCap.DepthTest);
GL.DepthFunc(DepthFunction.Less);
// Load the source of the vertex shader and compile it.
VertexShader = GL.CreateShader(ShaderType.VertexShader);
GL.ShaderSource(VertexShader, MyOpenglThings.VertexShaderSource);
GL.CompileShader(VertexShader);
// Load the source of the fragment shader and compile it.
FragmentShader = GL.CreateShader(ShaderType.FragmentShader);
GL.ShaderSource(FragmentShader, MyOpenglThings.FragmentShaderSource);
GL.CompileShader(FragmentShader);
// Create the shader program, attach the vertex and fragment shaders and link the program.
ShaderProgram = GL.CreateProgram();
GL.AttachShader(ShaderProgram, VertexShader);
GL.AttachShader(ShaderProgram, FragmentShader);
GL.LinkProgram(ShaderProgram);
// https://stackoverflow.com/questions/34068792/drawing-multiple-objects-in-opengl-with-different-buffers
// https://stackoverflow.com/questions/34072056/rendering-two-objects-with-opengl-and-vertex-array-objects
GL.GenVertexArrays(1, out VAO1);
GL.BindVertexArray(VAO1);
GL.GenVertexArrays(1, out VAO2);
GL.BindVertexArray(VAO2);
// Object 1 vertex positions
GL.GenBuffers(1, out object1_vertex_buffer);
GL.BindBuffer(BufferTarget.ArrayBuffer, object1_vertex_buffer);
GL.BufferData(BufferTarget.ArrayBuffer, object1_vertices.Length * sizeof(float), object1_vertices,BufferUsageHint.StaticDraw);
GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0);
// Object 1 vertex indices
GL.GenBuffers(1, out object1_index_buffer);
GL.BindBuffer(BufferTarget.ElementArrayBuffer, object1_index_buffer);
GL.BufferData(BufferTarget.ElementArrayBuffer, object1_indices.Length * sizeof(int), object1_indices, BufferUsageHint.StaticDraw);
GL.BindVertexArray(VAO2);
// Object 2 vertex positions
GL.GenBuffers(1, out object2_vertex_buffer);
GL.BindBuffer(BufferTarget.ArrayBuffer, object2_vertex_buffer);
GL.BufferData(BufferTarget.ArrayBuffer, object2_vertices.Length * sizeof(float), object2_vertices, BufferUsageHint.StaticDraw);
GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0);
// Object 2 vertex indices
GL.GenBuffers(1, out object2_index_buffer);
GL.BindBuffer(BufferTarget.ElementArrayBuffer, object2_index_buffer);
GL.BufferData(BufferTarget.ElementArrayBuffer, object2_indices.Length*sizeof(int), object2_indices, BufferUsageHint.StaticDraw);
}
我释放了分配的opengl资源（与我的问题无关，现在还没有调用）
private void CleanupOpenGL() {
// ...
}
}
我复制了着色器代码：
class MyOpenglThings
{
// A simple vertex shader possible. Just passes through the position vector.
public const string VertexShaderSource = @"
#version 330
layout(location = 0) in vec4 position;
void main(void)
{
gl_Position = position;
}
";
// A simple fragment shader. Just a constant red color.
public const string FragmentShaderSource = @"
#version 330
out vec4 outputColor;
void main(void)
{
outputColor = vec4(1.0, 0.0, 0.0, 1.0);
}
";
}
但是，当我启动程序时，我只会看到一个充满天蓝色的窗口。至少，opengl能够渲染背景色。但是我也想得到两个红色三角形。
那里有什么问题？如何在顶点数组对象中渲染两个网格？
答案 0 :(得分：2)
定义通用顶点属性数据（GL.VertexAttribPointer）的数组时，必须绑定应该存储定义的Vertex array object。
规范VAO2就是这种情况，但VAO1却不是，因为
GL.GenVertexArrays(1, out VAO1); GL.BindVertexArray(VAO1); GL.GenVertexArrays(1, out VAO2); GL.BindVertexArray(VAO2);
顶点数组对象VAO2已绑定。
此外，通用顶点属性数组必须由GL.EnableVertexAttribArray启用。启用或禁用顶点数组的状态也存储在顶点数组对象中：
GL.GenVertexArrays(1, out VAO1);
GL.BindVertexArray(VAO1);
// Object 1 vertex positions
GL.GenBuffers(1, out object1_vertex_buffer);
GL.BindBuffer(BufferTarget.ArrayBuffer, object1_vertex_buffer);
GL.BufferData(BufferTarget.ArrayBuffer, object1_vertices.Length * sizeof(float), object1_vertices,BufferUsageHint.StaticDraw);
GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0);
GL.EnableVertexAttribArray(0);
// [...]
GL.GenVertexArrays(1, out VAO2);
GL.BindVertexArray(VAO2);
// Object 2 vertex positions
GL.GenBuffers(1, out object2_vertex_buffer);
GL.BindBuffer(BufferTarget.ArrayBuffer, object2_vertex_buffer);
GL.BufferData(BufferTarget.ArrayBuffer, object2_vertices.Length * sizeof(float), object2_vertices, BufferUsageHint.StaticDraw);
GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0);
GL.EnableVertexAttribArray(0);
// [...]
答案 1 :(得分：0)
以上答案确实有帮助。 （我在这里发布，因为注释不适合代码。） 因此，我的加载代码现在看起来像：
private void glControl1_Load(object sender, EventArgs e) {
loaded = true;
GL.ClearColor(Color.SkyBlue);
GL.Enable(EnableCap.DepthTest);
GL.DepthFunc(DepthFunction.Less);
// Load the source of the vertex shader and compile it.
// ....
// Load the source of the fragment shader and compile it.
// ....
// Create the shader program, attach the vertex and fragment shaders and link the program.
// ....
GL.GenVertexArrays(1, out VAO1);
GL.BindVertexArray(VAO1);
// Object 1 vertex positions
GL.GenBuffers(1, out object1_vertex_buffer);
GL.BindBuffer(BufferTarget.ArrayBuffer, object1_vertex_buffer);
GL.BufferData(BufferTarget.ArrayBuffer, object1_vertices.Length * sizeof(float), object1_vertices,BufferUsageHint.StaticDraw);
GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0);
GL.EnableVertexAttribArray(0);
// Object 1 vertex indices
GL.GenBuffers(1, out object1_index_buffer);
GL.BindBuffer(BufferTarget.ElementArrayBuffer, object1_index_buffer);
GL.BufferData(BufferTarget.ElementArrayBuffer, object1_indices.Length * sizeof(int), object1_indices, BufferUsageHint.StaticDraw);
GL.GenVertexArrays(1, out VAO2);
GL.BindVertexArray(VAO2);
// Object 2 vertex positions
GL.GenBuffers(1, out object2_vertex_buffer);
GL.BindBuffer(BufferTarget.ArrayBuffer, object2_vertex_buffer);
GL.BufferData(BufferTarget.ArrayBuffer, object2_vertices.Length * sizeof(float), object2_vertices, BufferUsageHint.StaticDraw);
GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0);
GL.EnableVertexAttribArray(0);
// Object 2 vertex indices
GL.GenBuffers(1, out object2_index_buffer);
GL.BindBuffer(BufferTarget.ElementArrayBuffer, object2_index_buffer);
GL.BufferData(BufferTarget.ElementArrayBuffer, object2_indices.Length*sizeof(int), object2_indices, BufferUsageHint.StaticDraw);
}
GL.EnableVertexAttribArray的参数应与着色器程序中的值匹配。
还更改了一些几何坐标，因为三角形曾经重叠。