I am trying to render two triangles using separate Vertex Array objects. I am using OpenTK on C# (it provides almost the same API compared to defined OpenGL API). Here is my code:
I start from declaring my variables.
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 };
I do painting of every frame here:
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();
}
Here I do initialization of OpenGL arrays and buffers. I init here two Vertex Array Objects ( one for each triangle ), and two Buffers (for each) : vertices and indices. I set the proper length in bytes for them
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);
}
I free the allocated opengl resources (it does not relate to my question, it is not even called by now heh)
private void CleanupOpenGL() {
// ...
}
}
I have copied shader codes:
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);
}
";
}
But when I launch a program, I get only a window filled with SkyBlue Color. At least, opengl is capable of rendering background color. But I want to get two red triangles too.
What's wrong in there? How do I get rendering two meshes in Vertex Array Objects?
