CODEWITHSUNDEEP
c++openglglslblurpost-processing
Jose
Jose

Reputation: 127

Image blur effect in shaders

I want to do image effects such as screen blur in my game but I have a problem that it just darkens the screen slightly.

Here is the class for the FBO

GLuint m_fbo;
GLuint m_fboTexture;
GLuint m_fboDepthBuffer;

void FBO::Initialize(float width, float height)
{
    glGenFramebuffersEXT(1, &m_fbo);
    glGenTextures(1, &m_fboTexture);
    glGenRenderbuffersEXT(1, &m_fboDepthBuffer);

    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, m_fbo);

    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, m_fboTexture);
    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_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glGenerateMipmapEXT(GL_TEXTURE_2D);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, (GLuint)width, (GLuint)height, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
    glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, m_fboTexture, 0);

    glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, m_fboDepthBuffer);
    glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT24, (GLuint)width, (GLuint)height);
    glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, m_fboDepthBuffer);

    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);

    glDisable(GL_TEXTURE_2D);
}

void FBO::Bind()
{
    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, m_fbo);
}

void FBO::UnBind()
{
   glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
}

void FBO::Clear()
{
    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, m_fbo);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
}

This is how I set it up in my main class.

FBO m_fbo;//create an object

//initialize size
m_fbo.Initiliazie(screen_width, screen_height);

In my render function I do this

void Render()
{
   SetShaderProgram();//start shader program

   m_fbo.Bind();

   SetShaderImageSampler("texture", 0, m_fbo.m_fboTexture);
   SetShaderUniformVec2("size", (float)SCREEN_WIDTH, (float)SCREEN_HEIGHT);
   SetShaderUniformInt("kernel_size", ksize);

   //draws my texture
   m_spriteBatch->Draw(RecTangle(0, 0, (float)SCREEN_WIDTH, (float)SCREEN_HEIGHT));

   m_fbo.UnBind();

   EndShaderProgram();//end shader program
}

This is what SetShaderImageSampler function does:

void SetShaderImageSampler(char *sSamplerName, U32 nSlot, GLuint nHandle)
{
    glEnable(GL_TEXTURE_2D);
    glActiveTexture(GL_TEXTURE0 + nSlot);
    glBindTexture(GL_TEXTURE_2D, nHandle);
    U32 nSamplerLoc = glGetUniformLocation(m_shaderProgram, sSamplerName);
    glUniform1iARB(nSamplerLoc, nSlot);
}

This is my spritebatch draw

void SpriteBatch::Draw(RecTangle rect)
{
    //draws it depending on its center
    float left = -(rect.right/2.0f);
    float right = left + (rect.right);
    float top = -(rect.bottom/2.0f);
    float bottom = top + (rect.bottom);

    //vertices: Vertex(x, y, z, u, v) coordinates
    m_vertex[0] = Vertex(left,  top,    0, 0, 0);
    m_vertex[1] = Vertex(right, top,    0, 1, 0);
    m_vertex[2] = Vertex(right, bottom, 0, 1, 1);
    m_vertex[3] = Vertex(left,  bottom, 0, 0, 1);

    glEnableClientState(GL_VERTEX_ARRAY);
    glVertexPointer(3, GL_FLOAT, sizeof(Vertex), &m_vertex[0].m_fX);

    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
    glTexCoordPointer(2, GL_FLOAT, sizeof(Vertex), &m_vertex[0].m_fU);

    glDrawArrays(GL_QUADS, 0, 4);

    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);

    glColor4f(0.5f, 0.5f, 0.5f, 0.5f);
}

This is my frag shader

uniform sampler2D texture;
uniform vec2 size;
uniform int kernel_size;

void main (void)  
{ 
    vec4 color = vec4(0.0, 0.0, 0.0, 1.0);
    vec2 st = gl_TexCoord[0].st;
    vec2 texel = 1.0/size;

    int sum = 0;
    for(int i=-kernel_size; i <= kernel_size; i++) 
    {
            vec4 value = texture2D(texture, st + vec2(0.0, texel.y * i));
            int factor = kernel_size+1 - abs((float)i);
            color += value * factor;
            sum += factor;
    }
    color /= sum;

    gl_FragColor = color;
    gl_FragColor.a = 1.0;
}

Its not working too well. I tried changing the shader to do something else but it just slighly darkens it no matter what.

Upvotes: 3

Views: 1569

Answers (4)

Jose
Jose

Reputation: 127

Nevenmind I have it working now. I was calling Bind and UnBind in the wrong place.

Upvotes: 0

Graham McIntyre
Graham McIntyre

Reputation: 82

Ok, generally to do post processing effects you would render the scene with the frame buffer active. Then render a full screen quad with your post process (blur) shader active and the frame buffer textures bound as samplers.

Upvotes: 0

Graham McIntyre
Graham McIntyre

Reputation: 82

Maybe you haven't included enough code but I don't see you actually rendering anything in your Render method.

You have some calls the first of which I assume activate's the context, then you bind the frame buffer and link the shader variables, but next I would expect a call to render a quad / mesh somehow (i.e with a glBegin/glEnd section or a vertex buffer bind and render.)

Upvotes: 0

Mortennobel
Mortennobel

Reputation: 3481

The unbind should be

glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);

Upvotes: 2

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