Weird issue with GLSL Radial Blur - c++

Question

Shader used: http://www.gamerendering.com/2008/12/20/radial-blur-filter/
My issue is this: The whole scene only takes up a quarter of the screen space (which is a rectangle of these coordinates: width/2,0 width,height/2), and it seems to have been literally clipped (not scaled). It also rendered it with Y inverted (but I was able to fix this by removing the - sign from line 9's gl_Position.y).
I used this tutorial to do the post-processing, with the exception of using basic glBegin(GL_QUADS) instead of vertex arrays.
EDIT 2: I have tried using another shader (http://www.geeks3d.com/20110428/shader-library-swirl-post-processing-filter-in-glsl/), and it worked perfectly fine. No clipping.
EDIT: Here is the source of the shaders (I did some minor edits):
Fragment shader:
#version 140
// This texture should hold the image to blur.
// This can perhaps be a previous rendered scene.
uniform sampler2D tex;
// texture coordinates passed from the vertex shader
varying vec2 uv;
// some const, tweak for best look
const float sampleDist = 1.0;
const float sampleStrength = 20.2;
void main(void)
{
// some sample positions
float samples[10] =
float[](-0.08,-0.05,-0.03,-0.02,-0.01,0.01,0.02,0.03,0.05,0.08);
// 0.5,0.5 is the center of the screen
// so substracting uv from it will result in
// a vector pointing to the middle of the screen
vec2 dir = 0.5 - uv;
// calculate the distance to the center of the screen
float dist = sqrt(dir.x*dir.x + dir.y*dir.y);
// normalize the direction (reuse the distance)
//dir = dir/dist;
dir /= dist;
// this is the original colour of this fragment
// using only this would result in a nonblurred version
vec4 color = texture2D(tex,uv);
vec4 sum = color;
// take 10 additional blur samples in the direction towards
// the center of the screen
for (int i = 0; i < 10; i++)
{
sum += texture2D( tex, uv + dir * samples[i] * sampleDist );
}
// we have taken eleven samples
sum *= 1.0/11.0;
// weighten the blur effect with the distance to the
// center of the screen ( further out is blurred more)
float t = dist * sampleStrength;
t = clamp( t ,0.0,1.0); //0 <= t <= 1
//Blend the original color with the averaged pixels
gl_FragColor = mix( color, sum, t );
}
Vertex shader:
#version 140
varying vec2 uv;
// this vertex shader is from AMD RenderMonkey
void main(void)
{
gl_Position = vec4( gl_Vertex.xy, 0.0, 1.0 );
gl_Position = sign( gl_Position );
// Texture coordinate for screen aligned (in correct range):
uv = (vec2( gl_Position.x, gl_Position.y ) + vec2(1.0 )) / vec2( 2.0 );
}
Post-processor:
#include "std/opengl.h"
#include "postprocess.h"
Post::Post(Pos2D res) {
this->res = res;
glActiveTexture(GL_TEXTURE0);
glGenTextures(1, &this->texture);
glBindTexture(GL_TEXTURE_2D, this->texture);
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_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, res.x, res.y, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glBindTexture(GL_TEXTURE_2D, 0);
glGenRenderbuffers(1, &this->rbo);
glBindRenderbuffer(GL_RENDERBUFFER, this->rbo);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8, res.x, res.y);
glBindRenderbuffer(GL_RENDERBUFFER, 0);
glGenFramebuffers(1, &this->fbo);
glBindFramebuffer(GL_FRAMEBUFFER, this->fbo);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, this->texture, 0);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, this->rbo);
GLenum status;
if ((status = glCheckFramebufferStatus(GL_FRAMEBUFFER)) != GL_FRAMEBUFFER_COMPLETE) {
fprintf(stderr, "Framebuffer error! %i", status);
}
glBindFramebuffer(GL_FRAMEBUFFER, 0);
}
Post::~Post() {
glDeleteRenderbuffers(1, &this->rbo);
glDeleteTextures(1, &this->texture);
glDeleteFramebuffers(1, &this->fbo);
}
void Post::update(Pos2D res) {
this->res = res;
glBindTexture(GL_TEXTURE_2D, this->texture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, res.x, res.y, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glBindTexture(GL_TEXTURE_2D, 0);
glBindRenderbuffer(GL_RENDERBUFFER, this->rbo);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8, res.x, res.y);
glBindRenderbuffer(GL_RENDERBUFFER, 0);
}
void Post::bind() {
glBindFramebuffer(GL_FRAMEBUFFER, this->fbo);
}
void Post::unbind() {
glBindFramebuffer(GL_FRAMEBUFFER, 0);
}
void Post::render(Shader* shader) {
glClear(GL_COLOR_BUFFER_BIT);
glClearColor(0.0, 0.0, 0.0, 1.0);
shader->run();
auto tex = glGetUniformLocation(shader->program_handle, "tex");
glBindTexture(GL_TEXTURE_2D, this->texture);
glUniform1i(tex, 0);
glBegin(GL_QUADS);
glTexCoord2f(0.0, 0.0);
glVertex2f(0, 0);
glTexCoord2f(0.0, 1.0);
glVertex2f(0, this->res.y);
glTexCoord2f(1.0, 1.0);
glVertex2f(this->res.x, this->res.y);
glTexCoord2f(1.0, 0.0);
glVertex2f(this->res.x, 0);
glEnd();
glBindTexture(GL_TEXTURE_2D, 0);
glUseProgram(0);
}
Screenshot of the issue (as you can see, it's cut off):
Screenshot when I disable the shader (as you can see, it can render to the whole window, it is not clipped):

Answer 1

the problem comes from the way you define your vertex coordinates:
glTexCoord2f(0.0, 0.0);
glVertex2f(0, 0);
glTexCoord2f(0.0, 1.0);
glVertex2f(0, this->res.y);
glTexCoord2f(1.0, 1.0);
glVertex2f(this->res.x, this->res.y);
glTexCoord2f(1.0, 0.0);
glVertex2f(this->res.x, 0);
instead of using the window resolution as vertex coordinates, try drawing a quad with the following vertices: ( -1, -1 ), ( -1, 1 ), ( 1, 1 ) and ( 1, -1 ) - that would result in a full-screen quad in opengl's native coordinate system. in your vertex shader, it looks to me like your're trying to use the sign function to transform the vertex coords into this coordinate system:
gl_Position = vec4( gl_Vertex.xy, 0.0, 1.0 );
gl_Position = sign( gl_Position );
but of course then you'll get a quad with the corner points ( 0, 0 ), ( 0, 1 ), ( 1, 1 ) and ( 1, 0 ) instead, which explains why it only fills part of the screen.
And as a result, the texture coordinates that you calculate in your shader with this line:
uv = (vec2( gl_Position.x, gl_Position.y ) + vec2(1.0 )) / vec2( 2.0 );
are also wrong, resulting in the 'clipped' look you're experiencing - your texcoords range from 0.5 to 1, instead of 0 to 1. By the way, you explicitly define texcoords with glTexCoord2f anyway, and those are correct - so there's no need to calculate them again in the shader, just use the built-in gl_MultiTexcoord.