Simplest way to display a simple image in OpenGL (OpenTK)? - image

Question

I have to following code:
public void BeginDraw()
{
if(bufferMaterial != null)
{
bufferMaterial.Textures[0].Surface.BindFramebuffer();
beganDraw = true;
}
}
public void EndDraw()
{
if (beganDraw)
{
beganDraw = false;
GL.BindFramebuffer(FramebufferTarget.Framebuffer, 0);
if (bufferMaterial != null)
{
GL.BindBuffer(BufferTarget.ArrayBuffer, screenMesh.VBO);
GL.BindVertexArray(VAO);
GL.BindBuffer(BufferTarget.ElementArrayBuffer, screenMesh.VEO);
bufferMaterial.Use();
screenMesh.ApplyDrawHints(bufferMaterial.Shader);
GL.DrawElements(PrimitiveType.Triangles, 2, DrawElementsType.UnsignedInt, 0);
GL.BindBuffer(BufferTarget.ElementArrayBuffer, 0);
GL.BindVertexArray(0);
GL.BindBuffer(BufferTarget.ArrayBuffer, 0);
GL.UseProgram(0);
}
}
}
Between those two I draw my scene, so the image should be drawn to bufferMaterial.Textures[0].Surface.
Now the "screenMesh" is created like this:
screenMesh = new Mesh();
screenMesh.SetVertices(new float[] {
0,0,
1,0,
1,1,
0,1
});
screenMesh.SetIndices(new uint[] {
0,3,2,
0,1,2
});
screenMesh.SetDrawHints(new VertexObjectDrawHint("pos", 2, 2, 0));
-> 2 components, stride of 2, 0 offset
The shader looks like this:
++++++++
Screenbuffer
++++++++
[Shader vertexScreen]
#version 150 core
in vec2 pos;
uniform float _time;
uniform sampler2D tex;
void main() {
gl_Position = vec4(pos, -1, 1);
}
[Shader fragmentScreen]
#version 150 core
#define PI 3.1415926535897932384626433832795
out vec4 outColor;
uniform float _time;
uniform sampler2D tex;
//texture2D(tex,
void main() {
outColor = vec4(1,1,1,1);
}
Now, I would expect this to draw a white rectangle to the screen, but the screen stays black. I played around with the indices of the screenMesh a little so the might be off, but they were never visible...
I don't need any projection matrix with a shader like this right ?
Mesh class: http://pastebin.com/PcwEYqGH
Edit: Okay, the buffer is rendered now, but I still need to get the depth buffer working! The surface creation code looks like this:
public void Create(int width, int height, SurfaceFormat format)
{
Width = width;
Height = height;
textureHandle = GL.GenTexture();
//bind texture
GL.BindTexture(TextureTarget.Texture2D, textureHandle);
Log.Error("Bound Texture: " + GL.GetError());
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMinFilter, (int)TextureMinFilter.Nearest);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMagFilter, (int)TextureMagFilter.Nearest);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapS, (int)format.WrapMode);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapT, (int)format.WrapMode);
Log.Error("Created Texture Parameters: " + GL.GetError());
GL.TexImage2D(TextureTarget.Texture2D, 0, format.InternalFormat, Width, Height, 0, format.PixelFormat, format.SourceType, format.Pixels);
Log.Error("Created Image: " + GL.GetError());
//unbind texture
GL.BindTexture(TextureTarget.Texture2D, 0);
//create depthbuffer
if (format.DepthBuffer)
{
GL.GenRenderbuffers(1, out dbHandle);
GL.BindRenderbuffer(RenderbufferTarget.Renderbuffer, dbHandle);
GL.RenderbufferStorage(RenderbufferTarget.Renderbuffer, RenderbufferStorage.DepthComponent24, Width, Height);
}
//create fbo
fboHandle = GL.GenFramebuffer();
GL.BindFramebuffer(FramebufferTarget.Framebuffer, fboHandle);
GL.FramebufferTexture2D(FramebufferTarget.FramebufferExt, FramebufferAttachment.ColorAttachment0Ext, TextureTarget.Texture2D, textureHandle, 0);
if(format.DepthBuffer)
GL.FramebufferRenderbuffer(FramebufferTarget.FramebufferExt, FramebufferAttachment.DepthAttachment, RenderbufferTarget.Renderbuffer, dbHandle);
GL.BindFramebuffer(FramebufferTarget.Framebuffer, 0);
Log.Error("Created Framebuffer: " + GL.GetError());
}
And this is the code for binding it:
public void BindTexture(TextureUnit slot = TextureUnit.Texture0)
{
GL.ActiveTexture(slot);
GL.BindTexture(TextureTarget.Texture2D, textureHandle);
}
public void BindFramebuffer()
{
GL.BindFramebuffer(FramebufferTarget.Framebuffer, fboHandle);
}
Yet if the depth buffer is enabled, the screen goes black again.
EDIT: Forgot to clear the depth buffer!

Answer 1

There is a problem in your draw call:
GL.DrawElements(PrimitiveType.Triangles, 2, DrawElementsType.UnsignedInt, 0);
The second argument is the number of indices used for rendering. With only 2 indices, that's not enough for a complete triangle. You have 6 indices in your index array, so it should be:
GL.DrawElements(PrimitiveType.Triangles, 6, DrawElementsType.UnsignedInt, 0);
Beyond that, I haven't been able to find code or documentation for the Mesh class you are using, so I can't tell if the vertex data stored in the mesh is set up correctly.