Blur Shader: Can I use one Framebuffer for the horizontal and vertical pass?

Question

I have set up my blur shader with the following header:

#version 400
in vec2 texCoord;

uniform sampler2D u_texture;
uniform vec2 resolution;
uniform float radius;
uniform vec2 dir;

layout (location = 0) out vec4 out_color;
void main() { *some code*; out_color = vec4(*some code*); }

The vertical pass is working well but I would like to use the same Framebuffer for both passes.

My idea was to create Color Attachment1 and Color Attachment2. In the first pass, Attachment1 is the target (out_color) attachment. Now I want the second pass to bind Attachment1 to the sampler2D (u_texture) and write the resulting pixels (out_color) into Attachment2.

If there is any possibility to read from one Attachment and write to another, please let me know.

Thanks in advance!

Answer 1

Well, I tried a bit with glDrawBuffers and found a working solution.

Before the second pass starts, I simply switched the shader output:

layout (location = 0) out vec4 out_color;

to the second attachment (Attachment2) simply by writing:

GL.DrawBuffer(DrawBufferMode.ColorAttachment2);

This line of code will change the target of the 1st shader output (layout location = 0) so that it writes to Attachment2. Also, I restore the DrawBuffer after the second pass, so the first pass won't have any problems.