Fragmentshader and framebuffer solid colour

Question

Dear Stackoverflowers,

Lately I have been making my first baby steps in the world of shaders, using GLSL and openGL in C# with OpenTK, and I've stumbled into some problems which I seem to be unable to solve.

I started off with one shader program and some fast experimental shaders which worked fine, giving me the following result (just a green and red light circling a triangle):

Then I wanted to add some sort of glow to this and I heard you had to do this through applying a fragment shader to a texture. So I set out and rendered my scene to a framebuffer. I then bound the framebuffer texture and drew a quad. This showed me the same scene I had before, which meant it worked. Then to use the new fragmentshader I replace my first shader program with my new program after I wrote to the buffer and before writing the quad. Now the problem is that whatever I do the screen only gives one solid color, not doing any manipulations like I would like.

This is my drawing code:

    protected override void OnRenderFrame(FrameEventArgs e)
    {
        GL.Ext.BindFramebuffer(FramebufferTarget.FramebufferExt, fboID);
        GL.UseProgram(shaderProgramHandle);
        GL.PushAttrib(AttribMask.ViewportBit);
        {
            GL.Viewport(0, 0, 600, 600);

            // clear the screen in green, to make it very obvious what the clear affected. only the FBO, not the real framebuffer
            GL.ClearColor(0.0f, 0.0f, 0.0f, 1.0f);
            GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit | ClearBufferMask.StencilBufferBit);

            GL.PushAttrib(AttribMask.ColorBufferBit);

            // make sure no lingering textures are bound to draw vertices clearly.
            GL.BindTexture(TextureTarget.Texture2D, 0);

            GL.EnableVertexAttribArray(0);
            GL.BindBuffer(BufferTarget.ArrayBuffer, vbo);
            GL.VertexAttribPointer(0, 3, VertexAttribPointerType.Float, false, 0, 0);
            GL.DrawArrays(BeginMode.Triangles, 0, 3);

            GL.DisableVertexAttribArray(0);

            GL.Begin(BeginMode.Points);
            GL.Vertex3(lmp);
            GL.Vertex3(lmp2);
            GL.End();

            GL.PopAttrib();
        }
        GL.PopAttrib();

        GL.Ext.BindFramebuffer(FramebufferTarget.FramebufferExt, 0);

        angle += 0.01f;
        angle2 -= 0.017f;
        lmp = new Vector3((float)(2f * Math.Cos(angle)), (float)(Math.Sin(angle) * 2f), 0f);
        lmp2 = new Vector3((float)(2f * Math.Cos(angle2)), (float)(Math.Sin(angle2) * 2f), 0f);
        GL.Uniform3(uniformLmp, lmp);
        GL.Uniform3(uniformLmp2, lmp2);

        GL.UseProgram(secondProgram);
        GL.Enable(EnableCap.Texture2D);
        GL.ActiveTexture(TextureUnit.Texture0);
        GL.BindTexture(TextureTarget.Texture2D, fboTex);
        GL.Uniform1(GL.GetUniformLocation(secondProgram, "tex"), fboTex);

        GL.Clear(ClearBufferMask.ColorBufferBit);

        GL.Begin(BeginMode.TriangleStrip);

        GL.TexCoord2(.0f, .0f);
        GL.Vertex3(-1f, -1f, 0f);

        GL.TexCoord2(1.0f, .0f);
        GL.Vertex3(1f, -1f, 0f);

        GL.TexCoord2(.0f, 1.0f);
        GL.Vertex3(-1f, 1f, 0f);

        GL.TexCoord2(1.0f, 1.0f);
        GL.Vertex3(1f, 1f, 0f);

        GL.End();
        GL.Disable(EnableCap.Texture2D);
        GL.UseProgram(0);

        SwapBuffers();
    }

And these are my shaders:

//vertex shader
#version 330

layout (location = 0) in vec3 Position;
varying vec2 texCoord;

void main()
{
    gl_Position = vec4(Position.x, Position.y, Position.z, 1.0);
    texCoord = gl_TexCoord[0].st;
}

//fragment shader
#version 330

uniform sampler2D tex;
out vec4 FragColor;
varying vec2 texCoord;

void main()
{
    vec4 color = texture2D(tex, texCoord);
    color.r += 0.5f;
    FragColor = color;
}

This results in a solid red color, instead of giving the existing image a red hue.

Can anybody spot the problem here?

Is the image correctly displayed if you remove the `color.r += 0.5f;` line? If you lear OpenGL and GLSL i suggest to learn the core features of 3.2 and above and avoid deprecated parts (e.g. `varying` is deprecated) — t.niese, Jun 02 '13 at 11:04

score 0 · Accepted Answer · answered Jun 02 '13 at 15:44

0

It turns out that I forgot

GL.EnableClientState(ArrayCap.TextureCoordArray);

This meant that my UV coords were not passed to the shader, thus making it sample from just (0,0), explaining this wierd behaviour.

answered Jun 02 '13 at 15:44

Perry

98
7

Fragmentshader and framebuffer solid colour

1 Answers1