Shadow mapping, need help with framebuffer

OpenGL OpenGL: Advanced Coding
1

I’m developing a render engine for a work at the university, I’ve already implemented rendering, lightning, textures, and now I’m with shadows. To achieve shadows, I’m doing this: (I’m working with C# and OpenTK, which is a wrapper for C#, but the methods are the same)

// AT THE BEGINNING OF MY PROGRAM
// CREATE ANOTHER FRAMEBUFFER FOR DEPTH VALUES



// Framebuffer for shadow mapping
DepthFrameBuffer = GL.GenFramebuffer();
GL.BindFramebuffer(FramebufferTarget.Framebuffer, DepthFrameBuffer);

// texture for that framebuffer
int depthTexture;
depthTexture = GL.GenTexture();
GL.BindTexture(TextureTarget.Texture2D, depthTexture);
GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgb, 1024, 1024, 0, PixelFormat.Rgb, PixelType.Float, IntPtr.Zero);
GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.DepthComponent16, 1024, 1024, 0, PixelFormat.DepthComponent, PixelType.Float, IntPtr.Zero);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMagFilter, (float)TextureMagFilter.Nearest);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMinFilter, (float)TextureMinFilter.Nearest);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapS, (float)TextureWrapMode.ClampToEdge);
GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapT, (float)TextureWrapMode.ClampToEdge);

// link the texture to the framebuffer
GL.FramebufferTexture(FramebufferTarget.Framebuffer, FramebufferAttachment.DepthAttachment, depthTexture, 0);

// don't know exactly what this does
GL.DrawBuffer(DrawBufferMode.None);

and the shader for this is:


// VERTEX SHADER
#version 330 core

// Input vertex data, different for all executions of this shader.
layout(location = 0) in vec3 vertexPosition_modelspace;

// Values that stay constant for the whole mesh.
uniform mat4 depthMVP;

void main(){
      gl_Position =  depthMVP * vec4(vertexPosition_modelspace,1);
}



// FRAGMENT SHADER
#version 330 core

// Ouput data
layout(location = 0) out float fragmentdepth;

void main(){
      // Not really needed, OpenGL does it anyway
      fragmentdepth = gl_FragCoord.z;
}

// THEN, EVERY FRAME WHEN RENDERING:



public void DrawScene(Scene sc)
        {
            currentScene = sc;

            // Set shader for shadow mapping
            DepthShader.Use();
            // Set framebuffer for shadow mapping
            GL.BindFramebuffer(FramebufferTarget.Framebuffer, DepthFrameBuffer);

            // WHAT HERE??

            // Set shader to render scene
            Shader.Use();
            // Set normal framebuffer
            GL.BindFramebuffer(FramebufferTarget.Framebuffer, SceneFrameBuffer);

            // Calculate camera matrix
            mat4 camera = CameraMatrix();
            // Set scene background color
            SetClearColor(sc.BackgroundColor);
            // Draw scene
            DrawHierarchy(sc.Root.gameObject, camera.ToMatrix4(), persepctiveMat);*/
        }

So the question is: what do I do in (// WHAT HERE), in the code above? I’ve tried passing the vertices positions just like I do to render the scene normally, using the Ortho matrix instead of the perspective, and the light matrix instead of the camera matrix. But… I can’t see anything in the screen. So, I don’t know if I’m doing it right.

So three questions:

  • Is the code above right?
  • What must I do now to continue?
  • Once it’s done, how can I check if it’s right? (for example, rendering the depth map into the screen)
2

What’s going on with that first glTexImage2D? Looks like left-over copy/paste.

So the question is: what do I do in (// WHAT HERE), in the code above? I’ve tried passing the vertices positions just like I do to render the scene normally, using the Ortho matrix instead of the perspective, and the light matrix instead of the camera matrix. But… I can’t see anything in the screen. So, I don’t know if I’m doing it right.

So three questions:

  • Is the code above right?
  • What must I do now to continue?
  • Once it’s done, how can I check if it’s right? (for example, rendering the depth map into the screen)

To address your problem, I would implement the last of your questions first. That is, for now don’t do the second pass where you apply the shadow map to the scene in the camera frustum; just cast the scene into the shadow map (the first pass). To help verify that you are getting the shadow map output you want, use a very simple test scene (e.g. one cube in the middle of the light frustum). Then you can either glReadPixels() those depth values back to save to a disk image and view off-line, or even more conveniently do a simple 2nd pass that fills your screen with a single quad textured from your depth map (where you convert the 0…1 depth values into grey-scale color values). Once your reasonable satisfied that the first pass is working properly, add the second pass.