I draw a tile map on screen and each tile light(grayscale) in a FBO. All are quads.
I store the view in a Rect. To move I change de Rect, then I do this...
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(getViewRect().left,
getViewRect().left + getViewRect().width,
getViewRect().top + getViewRect().height,
getViewRect().top,
-1,
1);
glMatrixMode(GL_MODELVIEW);
I only draw the tiles inside the Rect.
The problem is the FBO. I have to draw the same tiles( the lights of the tiles), that are visible.
I want to know if there is a better way than, drawing the same tiles to the fbo with the offset of the tiles, drawing a smaller quad on the borders when is not completly visible, and changing texcoord, because when I draw outside the FBO, it draw on the opposite side.
I use FBO, because I apply shader to the lights.
It works perfect if I dont move the view, but if I move I dont know how to draw on the FBO.
You ought to be able to use glScissor to restrict all drawing within the FBO. Perform this operation after calling glBindBuffer(...) each time you bind it.
Hope this helps!
Related
I am using gluCylinder() to create a cylinder in openGL and then plotting points inside the cylinder with Depth Test On .
When i see the front view of the cylinder, the points inside the cylinder are obstructed by front face.
To make front face of the cylinder translucent i am using Blending.
I am using below functions.
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
But whatever coloring or alpha value i assign to the cylinder the front face is not looking transparent due to its back face.
Tell whether it is possible to do with blending only or else i need to introduce lighting for both the faces of Cylinder.Here it clearly visible the change in the color of front face and back face of cylinder. And the points inside the cylinder are not visible due to being obstructed by front face of cylinder.
You should be able to accomplish this by drawing the cylinder twice, while culling the front faces the first time, and culling the back faces the second time. This way, you can draw the front and back parts differently, e.g. by making the front part transparent.
The code sequence could look like this:
// Draw back part of cylinder, opaque.
glEnable(GL_CULL_FACE);
glCullFace(GL_FRONT);
gluCylinder(...);
// Draw points.
// Draw front part of cylinder, transparent.
glCullFace(GL_BACK);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
gluCylinder(...);
glDisable(GL_BLEND);
If I understand you right then no, you can't do it with blending alone.
If the cylinder's normals all point outward then you also won't be able to see the cylinder's internal parts no matter what you do.
I do something similar to show characters behind walls and it goes like this - render your scene normally and save it all to a framebuffer. Then render what you want shown behind with the buffer contents on top, using a custom shader to make a bubble of transparency around the thing you want shown behind.
Not sure if I am explaining it well or not but it unfortunately requires multiple steps to get the results you want.
Your problem is still a bit unclear to me despite the image but I will attempt to answer based on my perception of your issue.
You are drawing a cylinder and have geometry (lines or other models) inside the cylinder. You want the cylinder to look translucent so the inner objects are visible. Here is one way to do it. Assuming your render functions are drawCylinder() and drawPoints().
init()
{
...
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
...
}
drawScene()
{
glDepthMask(GL_FALSE);
glEnable(GL_BLEND);
drawCylinder();
glDisable(GL_BLEND);
glDepthMask(GL_TRUE);
drawPoints();
}
doing so will make sure that the points are drawn regardless of the cylinder. Try using lower values of alpha for your cylinder color.
Please note this is one way to do it. I suggest using shaders to have more control over blending as well as exploring fragment/pixel discard options.
I'm having an issue while using FBO.
My window size is 1200x300.
When I create a FBO that's 1200x300, everything is fine.
However, when I create FBO with 2400x600 size (effectively, two times bigger on both axes) and try to render the exact same primitives, I get used only one quarter of the FBO's actual area.
FBO same size as window:
FBO twice bigger (triangle clipping can be noticed):
I render these two triangles into FBO, then render a fullscreen quad with a FBO's texture over it. I clear FBO with this pine green color, so I know for sure that all that empty space on the second picture actually comes from the FBO.
// init() of the program
albedo = new RenderTarget(2400, 600, 24 /*depth*/); // in first case, params are 1200, 300, 24
// draw()
RenderTarget::set(albedo); // render to fbo
RenderTarget::clearColor(0.0f, 0.3f, 0.3f, 1.0f);
RenderTarget::clear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// render triangles ...
glDrawArrays(GL_TRIANGLES, 0, 6);
// now it's time to render a fullscreen quad
RenderTarget::set(); // render to back-buffer
RenderTarget::clearColor(0.3f, 0.0f, 0.0f, 1.0f);
RenderTarget::clear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, albedo->texture());
glUniform1i(albedoUnifLoc, 0);
RenderTarget::drawFSQ(); // draw fullscreen quad
I have no cameras of any kind, I don't use glViewport anywhere, I always send coordiantes of the primitives to be drawn in the unit-square space (both x and y coord are in [-1,1] range).
Question is, what am I doing wrong and how do I fix it?
Aside question is, is glViewport in any kind related to currently bound framebuffer? As far as I could understand, that function is just used to set the rectangle area on the window in which the drawing will occur.
Any suggestion would be greatly appreciated. I tried searching for the problem online, the only similar thing was in this SO question, but it hasn't helped me.
You need to call glViewport() with the size of your render target. The only time you can get away without calling it is when you render to the window, and the window is never resized. That's because the default viewport matches the initial window size. From the spec:
In the initial state, w and h are set to the width and height, respectively, of the window into which the GL is to do its rendering.
If you want to render to an FBO with a size different from your window, you have to call glViewport() with the size of the FBO. And when you go back to rendering to the window, you need to call glViewport() with the window size again.
The viewport dimensions are not per framebuffer state. I always thought that would have made sense, but it is not defined that way. So whenever you call glViewport(), you are changing global (i.e. per context) state, independent of the currently bound framebuffer.
I render two quads with OpenGL with equal z. When I have DEPTH enabled I get following image, but when it is off I get what I need one fruit over another. Is it possible to draw quads with equal z, as I want? My OGL settings:
glEnable(GL_BLEND); glEnable(GL_ALPHA_TEST); glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
EDIT sorry I forgot to mention that left topmost quad I call to render first, and I use orthographic
EDIT +1 when I render quads with different Z I get the same image, how to fix it?
The z-buffer doesn't care about transparency and so you have to sort the drawing order of your quads by their approximate depth.
I would change their depth to be different (you can use an orthographic projection to have them appear the same size) and then draw the further quad first.
Also, it is never a good idea to draw two polygons at the same depth even without transparency because of z-fighting.
I experimented and saw that I have same problem when I render cube, so the problem was because of vertices ordering, and possibly backface culling parameters.
I need to know how can I make the skybox appears as it's in the infinity??
I know that it's something related to depth, but I don't know the exact thing to disable or to enable??
First, turn off depth writes/testing (you don't need to bother with turning off depth testing if you draw the skybox first and clear your depth buffer):
glDisable(GL_DEPTH_TEST);
glDepthMask(false);
Then, move the camera to the origin and rotate it the inverse of the modelview matrix:
// assume we're working with the modelview
glPushMatrix();
// inverseModelView is a 4x4 matrix with no translation and a transposed
// upper 3x3 portion from the regular modelview
glLoadMatrix(&inverseModelView);
Now, draw your sky box and turn depth writes back on:
DrawSkybox();
glPopMatrix();
glDepthMask(true);
glEnable(GL_DEPTH_TEST);
You'll probably want to use glPush/PopAttrib() to ensure your other states get correctly set after you draw the skybox too (make sure to turn off things like lighting or blending if necessary).
You should do this before drawing anything so all color buffer writes happen on top of your sky box.
First, Clear the buffer.
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
Then, save your current modelview matrix and load the identity.
glPushMatrix();
glLoadIdentity();
Then render your skybox.
Skybox.render();
Then, clear the depth buffer and continue normally with rendering
glClear(GL_DEPTH_BUFFER_BIT);
OtherStuff.render();
glutSwapBuffers();
The only problem with drawing the sky box is first is that your pixel shader will execute for every pixel in the sky box. Just to be overwritten by other object in your world later on. Your best bet is to render all opaque object first then render your sky box. That way the pixel shader for the sky box only gets executed for the pixel who pass the z buffer test.
There is no infinity. A skybox is just a textured box, with normaly 0,0,0 in the middle.
Here is a short tut: link text
The best approach I can think of is to draw it on a first pass(or layer), then clear only the depth buffer. After that just draw the rest of the scene in another pass. This way the skybox will always remain "behind" the scene. Just remember to use the same camera for both passes and somehow snap the skybox to the camera.
I am rendering 4 vertices (a square) in front of a colored cube. The vertices are colored white, but are blended at 0.5f.
Related: Why does my colored cube not work with GL_BLEND?
Please could someone tell me why the colored cube appears brighter when obscured by the semi-opaque square?
Cube rendered without square in front:
Normal cube http://img408.imageshack.us/img408/2853/normalcube.png
And, rendered with the square:
Cube with square http://img142.imageshack.us/img142/6255/brightsquare.png
Please see the code used to create the colored cube, the code used to actually draw the cube, and the code where the cube and square are rendered.
This is the code in my init function:
glEnable(GL_CULL_FACE);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE);
I'd say it's because your semi-transparent square gets added to the existing pixels, thus incrementing their intensity.
The documentation for glBlendFunc() recommends setting the second parameter to GL_ONE_MINUS_SRC_ALPHA, that is the boilerplate for implementing transparency. Try it.