OpenGL only first texture render in fb0 - c

Question

I'm trying to attach two textures of Gaussian blur to a fbo in order to subtract them in the shader (return c2-c in dog) but the first texture gives strange results. I tried to find the problem but I do not see where it is. If anyone can enlighten me I would be very grateful. Thank you in advance.
Here is the C code:
static void draw(void) {
static int b1 = 0;
static int b2 = 50;
glBindFramebuffer(GL_FRAMEBUFFER, _fbo);
blur(_vao, b1, _tId, _fboTex[0], 1, 0);
glUseProgram(0);
blur(_vao, b2, _tId, _fboTex[0], 1, 1);
glUseProgram(0);
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
glBlitFramebuffer(0, 0, _dim[0], _dim[1], 0, 0, _dim[0], _dim[1], GL_COLOR_BUFFER_BIT, GL_NEAREST);
//glBlitFramebuffer(0, 0, _dim[0], _dim[1], _dim[0]/2, 0, _dim[0], _dim[1], GL_COLOR_BUFFER_BIT, GL_NEAREST);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
}
void tex_to_shader(GLuint tid, char * sampler_name, GLuint num_tex){
glActiveTexture(!num_tex ? GL_TEXTURE0 : GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, 0);
glUniform1i(glGetUniformLocation(blurPId, sampler_name), num_tex);
glBindTexture(GL_TEXTURE_2D, tid);
}
void blur(GLuint plate_vao, GLuint radius, GLuint in, GLuint out, GLuint nb_iterations, GLuint current_texture) {
int i, n;
GLuint temp, rin = in;
glGenTextures(1, &temp);
glBindTexture(GL_TEXTURE_2D, temp);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
radius = radius > MAX_RADIUS ? MAX_RADIUS : radius;
for(n = 0; n < (int)nb_iterations; n++) {
for(i = 0; i < 2; i++) {
glFramebufferTexture2D(GL_FRAMEBUFFER, !current_texture ? GL_COLOR_ATTACHMENT0 : GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D, i == 0 ? temp : out, 0);
glUseProgram(blurPId);
glUniform1i(glGetUniformLocation(blurPId, "inv"), i ? 1 : 0);
glUniform1fv(glGetUniformLocation(blurPId, "weight"), MAX_RADIUS, &weights[(radius * (radius - 1)) >> 1]);
glUniform2fv(glGetUniformLocation(blurPId, "offset"), MAX_RADIUS, (i % 2) ? offsetH : offsetV);
glUniform1i(glGetUniformLocation(blurPId, "nweights"), radius);
glDisable(GL_DEPTH_TEST);
glBindVertexArray(plate_vao);
tex_to_shader(rin, !current_texture ? "blur0" : "blur1", current_texture);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glBindVertexArray(0);
glBindTexture(GL_TEXTURE_2D, 0);
}
rin = out;
}
glDeleteTextures(1, &temp);
}
Here is our fragment shader:
#version 330
uniform sampler2D blur0;
uniform sampler2D blur1;
uniform int current_texture;
uniform int nweights;
uniform float weight[128];
uniform vec2 offset[128];
in vec2 vsoTexCoord;
out vec4 fragColor;
vec4 dog(sampler2D a, sampler2D b){
vec4 c = texture(a, vsoTexCoord.st) * weight[0];
vec4 c2 = texture(b, vsoTexCoord.st) * weight[0];
for (int i = 1; i < nweights; i++) {
c += texture(a, vsoTexCoord.st + offset[i]) * weight[i];
c += texture(a, vsoTexCoord.st - offset[i]) * weight[i];
c2 += texture(b, vsoTexCoord.st + offset[i]) * weight[i];
c2 += texture(b, vsoTexCoord.st - offset[i]) * weight[i];
}
return c;
}
vec4 gray(vec4 c){
float moyenne = 0.2126 * c.r + 0.7152 * c.g + 0.0722 * c.b;
return vec4(moyenne, moyenne, moyenne, 1.0);
}
void main(void) {
fragColor = dog(blur0,blur1);
//fragColor = gray(fragColor);
}

Answer 1

If you use a framebuffer with multiple color attachments, then you have to specify the color attachment(s), which should be written to. The color buffer(s) in which should be drawn, can be specified by glDrawBuffers.
e.g. If only should be drawn on GL_COLOR_ATTACHMENT1 the this can be specified like this:
GLenum attachment = GL_COLOR_ATTACHMENT1;
glDrawBuffers(1, &attachment);
In your case this mans you have to choose the proper color attachment at the begin of the function blur:
void blur(GLuint plate_vao, GLuint radius, GLuint in, GLuint out,
GLuint nb_iterations, GLuint current_texture) {
GLenum attachment = !current_texture ? GL_COLOR_ATTACHMENT0 : GL_COLOR_ATTACHMENT1;
glDrawBuffers(1, &attachment);
.....
}