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kloye

OpenGL GLSL - FBO - render to texture - Image Processing

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Hi all,

I'm currently trying to implement in OpenGL image processing algorithms.

I would like to successively use several shaders in order to perform several filters (Sobel Gaussian,...).
I understood that to do thius I had to render to texture thanks to a FBO. I read a lot of things about that, and wrote a code. But I'm not getting the result I expected.

For the moment, I'm just trying to use two shaders. So, I have an original image which is the input of my first shader. Then, I want to render the output of the shader to a texture which will then be the input of my second shader (pingpong technique). And finally, I want to display the output of the second shader.

But as result, I'm getting the original image.

My code is the following:



/******************** Shaders Function *******************************/
void setupShaders(char *vert, char *frag, GLuint p) {
GLuint v, f;
char *vs = NULL,*fs = NULL;
v = glCreateShader(GL_VERTEX_SHADER);
f = glCreateShader(GL_FRAGMENT_SHADER);
vs = textFileRead(vert);
fs = textFileRead(frag);
const char * ff = fs;
const char * vv = vs;
glShaderSource(v, 1, &vv, NULL);
glShaderSource(f, 1, &ff, NULL);
free(vs);free(fs);
glCompileShader(v);
glCompileShader(f);
p = glCreateProgram();
glAttachShader(p,f);
glAttachShader(p,v);
glLinkProgram(p);
glUseProgram(p);
}
/******************** Texture Function ***********************************/
void setupTexture(void) {
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
}
/******************** Quad Drawing Function ******************************/
void ShaderDraw(void){
glBegin(GL_QUADS);
glTexCoord2f(0.0, 0.0); glVertex3f(0.0, 0.0, 0.0);
glTexCoord2f(0.0, 1.0); glVertex3f(0.0, height, 0.0);
glTexCoord2f(1.0, 1.0); glVertex3f(width, height, 0.0);
glTexCoord2f(1.0, 0.0); glVertex3f(width, height, 0.0);
glEnd();
}

/******************** Initialization Function ***************************/
void init(void)
{
//Checking GLSL
glewInit();
if (glewIsSupported("GL_VERSION_2_0"))
printf("Ready for OpenGL 2.0\n");
else {
printf("OpenGL 2.0 not supported\n");
exit(1);
}

// Init
glClearColor (0.0, 0.0, 0.0, 0.0);
glShadeModel(GL_FLAT);
glEnable(GL_DEPTH_TEST);
}
/******************** Display Function **********************************/
void display(void)
{
glEnable(GL_TEXTURE_2D);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);

glBegin(GL_QUADS);
glTexCoord2f(0.0, 0.0); glVertex3f(-4.0, -4.0, 0.0);
glTexCoord2f(0.0, 1.0); glVertex3f(-4.0, 4.0, 0.0);
glTexCoord2f(1.0, 1.0); glVertex3f(4.0, 4.0, 0.0);
glTexCoord2f(1.0, 0.0); glVertex3f(4.0, -4.0, 0.0);
glEnd();

glFlush();
glDisable(GL_TEXTURE_2D);
}
/******************** Reshape Function *********************************/
void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0, (GLfloat) w/(GLfloat) h, 1.0, 100.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0, 0.0, -7.0);
}
/******************** Main Function *************************************/
int main(int argc, char** argv)
{
// Glut Initialisation
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
// Window Generation
glutInitWindowSize(1000,800);
glutInitWindowPosition(100, 100);
glutCreateWindow("Night Vision");

// Initialisation Function
init();

// Downloading Image
data = cLoadBitmap("lena.bmp", &height, &width);
checkGLErrors ("Downloading Image");

int read_tex = 0;
int write_tex = 1;

// Generating Texture
glEnable(GL_TEXTURE_2D);
glGenTextures(2, texImg);
// Init Texture0
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texImg[read_tex]);
setupTexture();
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
checkGLErrors ("InitTexture0");
// Init Texture1
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, texImg[write_tex]);
setupTexture();
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
checkGLErrors ("InitTexture1");

// Setup Framebuffer Object
GLuint fb;
glGenFramebuffersEXT(1, &fb);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fb);
checkGLErrors ("Framebuffer->fb");

GLenum att_point[] = {GL_COLOR_ATTACHMENT0_EXT, GL_COLOR_ATTACHMENT1_EXT};
glBindTexture(GL_TEXTURE_2D, texImg[read_tex]);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, att_point[read_tex], GL_TEXTURE_2D, texImg[read_tex], 0);
glBindTexture(GL_TEXTURE_2D, texImg[write_tex]);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, att_point[write_tex], GL_TEXTURE_2D, texImg[write_tex], 0);
checkFramebufferStatus();

//set the write texture as output buffer for the shader
glDrawBuffer(att_point[write_tex]);

// create, init and enable the shader
setupShaders("filter.vert", "sobel_filter_3.frag", p1);
checkGLErrors ("Shaders 1");
// attach the input texture(read texture) to the first texture unit
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D,texImg[read_tex]);
GLuint texLoc;
texLoc = glGetUniformLocation(p1,"tex");
glUniform1i(texLoc, 0);
// draw a square with the texture on it so to perform the computation
ShaderDraw();

// swap the buffers
read_tex = 1;
write_tex = 0;

// Delete program 1
glDeleteProgram(p1);

// set the write texture as output buffer for the shader
glDrawBuffer(att_point[write_tex]);
// create, init and enable the shaders
setupShaders("filter.vert", "gaussian7.frag", p2);
checkGLErrors ("Shaders 2");
// attach the input texture(read texture) to the first texture unit
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D,texImg[read_tex]);
texLoc = glGetUniformLocation(p2,"tex");
glUniform1i(texLoc, 0);
// draw a square with the texture on it so to perform the computation
ShaderDraw();

// Delete program 2 & disable the FBO
glDeleteProgram(p2);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
glUseProgram(0);

// Bind the texture to display
glBindTexture(GL_TEXTURE_2D,texImg[0]);

// Glut Functions: Display, Reshape, Keyboard
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutKeyboardFunc(keyboard);
// Calling Main
glutMainLoop();
return 0;
}


Does someone have an idea of what is wrong???
I really need some help!

Thanks

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Thanks for your interest.

My vertex shader is:

void main() {

gl_TexCoord[0] = gl_MultiTexCoord0;

gl_Position = ftransform();

}

My fragment shaders are :

Sobel_filter_3:

#define KERNEL_SIZE 9
uniform sampler2D tex;
ivec2 image_size = textureSize(tex, 0);
const float kernel_h[KERNEL_SIZE] = {
1, 0, -1,
2, 0, -2,
1, 0, -1
};
const float kernel_v[KERNEL_SIZE] = {
1, 2, 1,
0, 0, 0,
-1, -2, -1
};
const float step_w = 1.0/image_size[0];
const float step_h = 1.0/image_size[1];
const vec2 offset[KERNEL_SIZE] = {
vec2(-step_w, -step_h), vec2(0.0, -step_h), vec2(step_w, -step_h),
vec2(-step_w, 0.0), vec2(0.0, 0.0), vec2(step_w, 0.0),
vec2(-step_w, step_h), vec2(0.0, step_h), vec2(step_w, step_h)
};
void main(void)
{
int i = 0;
vec4 sum_h = vec4(0.0);
vec4 sum_v = vec4(0.0);
vec4 sum = vec4(0.0);
vec4 two = vec4(2.0);

for( i=0; i<KERNEL_SIZE; i++ )
{
vec4 tmp = texture2D(tex, gl_TexCoord[0].st + offset);
sum_h += tmp * kernel_h / 2;
sum_v += tmp * kernel_v / 2;
}
sum = sqrt(pow(sum_h,two) + pow(sum_v,two));
gl_FragColor = sum ;
}

Gaussian7:

#define KERNEL_SIZE 49
uniform sampler2D tex;
ivec2 image_size = textureSize(tex, 0);
const float kernel_h[KERNEL_SIZE] = {
1, 1, 1, 1, 1, 1, 1,
1, 2, 2, 2, 2, 2, 1,
1, 2, 3, 4, 3, 2, 1,
1, 2, 4, 8, 4, 2, 1,
1, 2, 3, 4, 3, 2, 1,
1, 2, 2, 2, 2, 2, 1,
1, 1, 1, 1, 1, 1, 1
};
const float step_w = 1.0/image_size[1];
const float step_h = 1.0/image_size[0];

const vec2 offset[KERNEL_SIZE] = {
vec2(-3*step_w, -3*step_h), vec2(-2*step_w, -3*step_h), vec2(-step_w, -3*step_h), vec2(0.0, -3*step_h), vec2(step_w, -3*step_h), vec2(2*step_w, -3*step_h), vec2(3*step_w, -3*step_h),
vec2(-3*step_w, -2*step_h), vec2(-2*step_w, -2*step_h), vec2(-step_w, -2*step_h), vec2(0.0, -2*step_h), vec2(step_w, -2*step_h), vec2(2*step_w, -2*step_h), vec2(3*step_w, -2*step_h),
vec2(-3*step_w, -1*step_h), vec2(-2*step_w, -1*step_h), vec2(-step_w, -1*step_h), vec2(0.0, -1*step_h), vec2(step_w, -1*step_h), vec2(2*step_w, -1*step_h), vec2(3*step_w, -1*step_h),
vec2(-3*step_w, 0.0), vec2(-2*step_w, 0.0), vec2(-step_w, 0.0), vec2(0.0, 0.0), vec2(step_w, 0.0), vec2(2*step_w, 0.0), vec2(3*step_w, 0.0),
vec2(-3*step_w, 1*step_h), vec2(-2*step_w, 1*step_h), vec2(-step_w, 1*step_h), vec2(0.0, 1*step_h), vec2(step_w, 1*step_h), vec2(2*step_w, 1*step_h), vec2(3*step_w, 1*step_h),
vec2(-3*step_w, 2*step_h), vec2(-2*step_w, 2*step_h), vec2(-step_w, 2*step_h), vec2(0.0, 2*step_h), vec2(step_w, 2*step_h), vec2(2*step_w, 2*step_h), vec2(3*step_w, 2*step_h),
vec2(-3*step_w, 3*step_h), vec2(-2*step_w, 3*step_h), vec2(-step_w, 3*step_h), vec2(0.0, 3*step_h), vec2(step_w, 3*step_h), vec2(2*step_w, 3*step_h), vec2(3*step_w, 3*step_h)
};

void main(void)
{
int i = 0;
vec4 sum_h = vec4(0.0);
vec4 sum_v = vec4(0.0);
vec4 sum = vec4(0.0);
vec4 two = vec4(2.0);

for( i=0; i<KERNEL_SIZE; i++ )
{
vec4 tmp = texture2D(tex, gl_TexCoord[0].st + offset);
sum_h += tmp * kernel_h / 100;
sum_h.a = 1.0;
}
gl_FragColor = sum_h;
}

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Try making things simpler by creating a basic shader program that always sets the gl_FragColor to red or something to verify that your shader programs are executing properly.

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My shaders are working separately. I tried them with a code without fbo and they are working.
I also tried this code with simple shaders (glFragColor = vec4(1.0, 0.0, 0.0, 0.0)), and i'm still getting the original image.

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Quote:
vec4(1.0, 0.0, 0.0, 0.0)

Thats because u give invisible color(alpha==0) :)
give there more than 0.0 (maybe 0.5 or 1.0)

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With glFragColor = vec4(1.0, 0.0, 0.0, 1.0) for both shader, I'm still getting the original image as final result except in the top right corner which is red.

I have no idea of what is wrong and I really need some help!!

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U propaby modify somewhere your frag color because with only this:

///////////VERT:
void main() {

gl_TexCoord[0] = gl_MultiTexCoord0;

gl_Position = ftransform();

}
//////////////FRAG
void main()
{
gl_FragColor=vec4(1,0,0,1);
}

You should have all quad red.

Next:
Quote:
glBegin(GL_QUADS);
glTexCoord2f(0.0, 0.0); glVertex3f(0.0, 0.0, 0.0);
glTexCoord2f(0.0, 1.0); glVertex3f(0.0, height, 0.0);
glTexCoord2f(1.0, 1.0); glVertex3f(width, height, 0.0);
glTexCoord2f(1.0, 0.0); glVertex3f(width, height, 0.0);//<<<<MISTAKE
glEnd();

There should be 0

Another quastion: do u have cull face on CCW or CW?

Next one:
where are u setting up mipmapping?

Edit:
what GL and FBO errors do u get?

Edit2:
plz stop using glut... It`s so old

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I've noticed the mistake in the quad drawing and I've modified it. Now, I'm getting the original image except in the top right corner where I get a red rectangle. I've also noticed that if I comment the line glUseProgram(0) the whole image is processed by the first shader and the small rectangle is still red. In addition, it seems that the rectangle doesn't have the right input.

--Another question: do u have cull face on CCW or CW?
I have no idea. How can I figure it out?

--where are u setting up mipmapping?
I'm not. Should I? Why?

--what GL and FBO errors do u get?
I get an error after the setup of the second shader("shader 2").

--plz stop using glut... It`s so old
I didn't know it. What should I use instead?


I really need some help. I'm completely stuck in my project because of that.
If you have any other ideas that can allow me to read back the data to implement successive shaders, I'd appreciate to know them.

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Just to let you know that I figured it out.

It was a problem with the definition of the glVertex3f in drawing the quad.

In the display function :

glBegin(GL_QUADS);
glTexCoord2f(0.0, 0.0); glVertex3f(-0.5, -0.5, 0.0);
glTexCoord2f(0.0, 1.0); glVertex3f(-0.5, 0.5, 0.0);
glTexCoord2f(1.0, 1.0); glVertex3f(0.5, 0.5, 0.0);
glTexCoord2f(1.0, 0.0); glVertex3f(0.5, -0.5, 0.0);
glEnd();

and for the shaderDraw function:

glBegin(GL_QUADS);
glTexCoord2f(0.0, 0.0); glVertex3f(-1.0, -1.0, 0.0);
glTexCoord2f(0.0, 1.0); glVertex3f(-1.0, 1.0, 0.0);
glTexCoord2f(1.0, 1.0); glVertex3f(1.0, 1.0, 0.0);
glTexCoord2f(1.0, 0.0); glVertex3f(1.0, -1.0, 0.0);
glEnd();

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      //"camera" is the camera which was used for rendering the normal buffer renderer.setUniform4m(ressources->shaderSSAO->getUniform("uNormalViewMatrix"), glmExt::createViewMatrix(glm::vec3(0,0,0),camera.getForward(),camera.getUp())//parameters are (position,forwardVector,upVector) ); Though i have the feeling this is the wrong approach. Is this right or is there a better/correct way of transforming a world space normal into viewspace?
    • By HawkDeath
      Hi,
      I'm trying mix two textures using own shader system, but I have a problem (I think) with uniforms.
      Code: https://github.com/HawkDeath/shader/tree/test
      To debug I use RenderDocs, but I did not receive good results. In the first attachment is my result, in the second attachment is what should be.
      PS. I base on this tutorial https://learnopengl.com/Getting-started/Textures.


    • By norman784
      I'm having issues loading textures, as I'm clueless on how to handle / load images maybe I missing something, but the past few days I just google a lot to try to find a solution. Well theres two issues I think, one I'm using Kotlin Native (EAP) and OpenGL wrapper / STB image, so I'm not quite sure wheres the issue, if someone with more experience could give me some hints on how to solve this issue?
      The code is here, if I'm not mistaken the workflow is pretty straight forward, stbi_load returns the pixels of the image (as char array or byte array) and you need to pass those pixels directly to glTexImage2D, so a I'm missing something here it seems.
      Regards
    • By Hashbrown
      I've noticed in most post processing tutorials several shaders are used one after another: one for bloom, another for contrast, and so on. For example: 
      postprocessing.quad.bind() // Effect 1 effect1.shader.bind(); postprocessing.texture.bind(); postprocessing.quad.draw(); postprocessing.texture.unbind(); effect1.shader.unbind(); // Effect 2 effect2.shader.bind(); // ...and so on postprocessing.quad.unbind() Is this good practice, how many shaders can I bind and unbind before I hit performance issues? I'm afraid I don't know what the good practices are in open/webGL regarding binding and unbinding resources. 
      I'm guessing binding many shaders at post processing is okay since the scene has already been updated and I'm just working on a quad and texture at that moment. Or is it more optimal to put shader code in chunks and bind less frequently? I'd love to use several shaders at post though. 
      Another example of what I'm doing at the moment:
      1) Loop through GameObjects, bind its phong shader (send color, shadow, spec, normal samplers), unbind all.
      2) At post: bind post processor quad, and loop/bind through different shader effects, and so on ...
      Thanks all! 
    • By phil67rpg
      void collision(int v) { collision_bug_one(0.0f, 10.0f); glutPostRedisplay(); glutTimerFunc(1000, collision, 0); } void coll_sprite() { if (board[0][0] == 1) { collision(0); flag[0][0] = 1; } } void erase_sprite() { if (flag[0][0] == 1) { glColor3f(0.0f, 0.0f, 0.0f); glBegin(GL_POLYGON); glVertex3f(0.0f, 10.0f, 0.0f); glVertex3f(0.0f, 9.0f, 0.0f); glVertex3f(1.0f, 9.0f, 0.0f); glVertex3f(1.0f, 10.0f, 0.0f); glEnd(); } } I am using glutTimerFunc to wait a small amount of time to display a collision sprite before I black out the sprite. unfortunately my code only blacks out the said sprite without drawing the collision sprite, I have done a great deal of research on the glutTimerFunc and  animation.
    • By Lewa
      So, i stumbled upon the topic of gamma correction.
      https://learnopengl.com/Advanced-Lighting/Gamma-Correction
      So from what i've been able to gather: (Please correct me if i'm wrong)
      Old CRT monitors couldn't display color linearly, that's why gamma correction was nessecary. Modern LCD/LED monitors don't have this issue anymore but apply gamma correction anyway. (For compatibility reasons? Can this be disabled?) All games have to apply gamma correction? (unsure about that) All textures stored in file formats (.png for example) are essentially stored in SRGB color space (as what we see on the monitor is skewed due to gamma correction. So the pixel information is the same, the percieved colors are just wrong.) This makes textures loaded into the GL_RGB format non linear, thus all lighting calculations are wrong You have to always use the GL_SRGB format to gamma correct/linearise textures which are in SRGB format  
      Now, i'm kinda confused how to proceed with applying gamma correction in OpenGL.
      First of, how can i check if my Monitor is applying gamma correction? I noticed in my monitor settings that my color format is set to "RGB" (can't modify it though.) I'm connected to my PC via a HDMI cable. I'm also using the full RGB range (0-255, not the 16 to ~240 range)
       
      What i tried to do is to apply a gamma correction shader shown in the tutorial above which looks essentially like this: (it's a postprocess shader which is applied at the end of the renderpipeline)
      vec3 gammaCorrection(vec3 color){ // gamma correction color = pow(color, vec3(1.0/2.2)); return color; } void main() { vec3 color; vec3 tex = texture2D(texture_diffuse, vTexcoord).rgb; color = gammaCorrection(tex); outputF = vec4(color,1.0f); } The results look like this:
      No gamma correction:
      With gamma correction:
       
      The colors in the gamma corrected image look really wased out. (To the point that it's damn ugly. As if someone overlayed a white half transparent texture. I want the colors to pop.)
      Do i have to change the textures from GL_RGB to GL_SRGB in order to gamma correct them in addition to applying the post process gamma correction shader? Do i have to do the same thing with all FBOs? Or is this washed out look the intended behaviour?
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