Develop Reference

LibGDX - Basic 2D lighting, don't know what to do

It's my first time attempting to create a basic light system that uses a black texture with a white circle on top. I read various threads about the issue but I just don't know what I am doing wrong.
What I want is the ambient to be dark and the light to be well white but changing the spritebatch color to something darker will cause the light to be darker to EVEN if I reset the color when drawing the light texture
So this is what I want (did this by forcing the light texture draw 5 times but that isn't a solution, it's an hack):
This is what I get (only 1 light texture is drawn but isn't very visible):
This is what I get without darkening the spritebatch:
Main code:
Game.sb.begin();
//Make stuff darker
Game.sb.setColor(0.1f, 0.1f, 0.1f,1f);
sb.setBlendFunction(GL20.GL_SRC_ALPHA, GL20.GL_ONE_MINUS_SRC_ALPHA);
lvl.render();
//Reset color
Game.sb.setColor(1f, 1f, 1f,1f);
sb.setBlendFunction(GL20.GL_DST_COLOR, GL20.GL_SRC_ALPHA);
//This draws all lights by drawing a texture with the above blending function
lightM.render();
Game.sb.end();
Light object draw method:
Game.sb.setColor(c.r,c.b,c.g, 1f);
Utils.drawTexture(Assets.get("sprites/lightcircle2.png", Texture.class), pos, size, true);
Game.sb.setColor(1,1,1,1);
Am I making some kind of error with the setcolor? I been considering using a FrameBuffer but I am not sure if it will give me the light effect I want
By the way this is my light texture (it's CC0):

You can achieve your requirement by these ways :
By using Shaders. Here is a small video and article on that video.
By use FBO and Blending, Here is one of my answer on this topic.
You can use box2dlight, even without using box2dbody(if you don't want any shadows)
World world = new World(new Vector2(0,0),false);
RayHandler rayHandler = new RayHandler(world);
rayHandler.setCombinedMatrix(stage.getCamera().combined); //<-- pass your camera combined matrix
new PointLight(rayHandler,1000, Color.WHITE,radius,x_position,y_position);
And at last call rayHandler.updateAndRender(); after all your rendering in your render() method.

OpenGL blending: Remove pixels being drawn over (immediate mode)

What I'd like to achieve is a blend where I draw two quads over eachother, both transparent, and the quad drawn last will cancel the colour of the previous quad completely, as if it was never there. However, it may not affect anything behind it besides that single other quad. Because I'm horrible at explaining, I made the following image:
I'm using very basic openGL immediate mode functions.
Currently I have something along the lines of:
glEnable(GL_BLEND)
glColor4f(0,0,1,0.3f);
glBegin(GL_QUADS);
{
glVertex2d(100, -100);
glVertex2d(-100, -100);
glVertex2d(-100, 100);
glVertex2d(100, 100);
}
glEnd();
glColor4f(0,1,0,0.3f);
glBegin(GL_QUADS);
{
glVertex2d(150, -50);
glVertex2d(-50, -50);
glVertex2d(-50, 150);
glVertex2d(150, 150);
}
glEnd();

This isn't really a blending problem per se.
One way to solve this would be to change the depth buffer comparison function.
Use GL_LESS for the green square, while drawing the blue square first.
This way the pixels of the green square overlapping the blue square, simply wouldn't be drawn at all to begin with.
glDepthFunc(GL_LEQUAL);
// Draw the blue square
glDepthFunc(GL_LESS);
// Draw the green square
If you want to have elements visible under both the blue and green square. You could draw the first and then clear the depth buffer and then it's the same.
glDepthFunc(GL_LEQUAL);
// Draw the red squares
glClear(GL_DEPTH_BUFFER_BIT);
glDepthFunc(GL_LEQUAL);
// Draw the blue square
glDepthFunc(GL_LESS);
// Draw the green square
Whether there's a simpler way to do it, depends on what the overall goal is.

Slick2d / LWJGL Adjusting alpha channel in OpenGL layer ( Java )

I apologize for some of my ignorance as I am fairly new to Slick2D and LWJGL. Essentially what I'm trying to do is make a scene look like night time by covering it with a GL_QUADS rectangle that is tinted blue and is translucent.
That part is easy enough. What I want to do from there is draw triangles into this layer that vary the alpha channel so. The reason I want to do this is so I can simulate a light source by decreasing the opacity of the blue tinted rectangle as it gets closer to the light source.
I drew an example of what the expected result should be with the green being the background, the blue being the nighttime effect created by a blue tinted rectangle, and the increasingly dim light source in the center.
I need to find a way to do this with triangles because I created a raycasting algorithm that generates the result as a series of gradient triangles.
I apologize if this is explained poorly. I will answer any questions you might have.
Here is the chunk of code used to create the blue tinted rectangle:
glColor4f (0.0f,0.0f,1.0f,0.4f);
glBegin(GL_QUADS);
glVertex2f(0,0);
glVertex2f(screenWidth,0);
glVertex2f(screenWidth,screenHeight);
glVertex2f(0,screenHeight);
glEnd();
I would like to write a modified version of the following code to adjusted the alpha channel of that rectangle.
glBegin(GL_TRIANGLES);
setAlphaOfPriorLayer(0.0f);
glVertex2f(x1,y1);
setAlphaOfPriorLayer(0.4f);
glVertex2f(x2,y2);
setAlphaOfPriorLayer(0.4f);
glVertex2f(x3,y3);
glEnd();
Again, I'm using triangles to approximate a circle and allow for proper raycasting.

To achieve this, the use of a Frame Buffer Object is super useful. A FBO allows you to essentially render to a texture which can then be displayed on the screen. In my particular case, I rendered the elements to a FBO then used a shader while drawing it to the screen to get the desired opacities.

Drawing a partially transparent Pixmap to a Texture (libgdx)

Using libgdx, is there something we have to do to enable transparency drawing a Pixmap to a Texture? I've tried doing this before the texture's draw() call where I pass the Pixmap:
Gdx.gl.glClearColor(0.5f, 0.0f, 0.0f, 1.0f);
Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
Gdx.gl.glEnable(GL10.GL_BLEND);
But it's painting an opaque dark red (glClearColor) color instead of a transparent pixel.

I don't know the reason for the lack of transparency drawing to a Texture, but it appears that using Pixmaps exclusively (drawing a pixmap onto another larger pixmap) and only rendering to the Texture as a very last step was the solution.
Can't find information on it so I can only assume that drawing a transparent Pixmap to a Texture to blend with the Texture's background color isn't supported.

OpenGL - Unable to render colors other than white after texture mapping

I'm trying to render a colored cube after rendering other cubes that have textures. I have multiple "Drawer" objects that conform to the Drawer interface, and I pass each a reference to the GL object to the draw( final GL gl ) method of each individual implementing class. However, no matter what I do, I seem unable to render a colored cube.
Code sample:
gl.glDisable(GL.GL_TEXTURE_2D);
gl.glColor3f( 1f, 0f, 0f );
gl.glBegin(GL.GL_QUADS);
// Front Face
Point3f point = player.getPosition();
gl.glNormal3f(0.0f, 0.0f, 1.0f);
//gl.glTexCoord2f(0.0f, 0.0f);
gl.glVertex3f(-point.x - 1.0f, -1.0f, -point.z + 1.0f);
//gl.glTexCoord2f(1.0f, 0.0f);
gl.glVertex3f(-point.x + 1.0f, -1.0f, -point.z + 1.0f);
//continue rendering rest of cube. ...
gl.glEnd();
gl.glEnable(GL.GL_TEXTURE_2D);
I've also tried throwing the glColor3f calls before each vertex call, but that still gives me a white cube. What's up?

There are a few things you need to make sure you do.
First off:
gl.glEnable(gl.GL_COLOR_MATERIAL);
This will let you apply colors to your vertices. (Do this before your calls to glColor3f.)
If this still does not resolve the problem, ensure that you are using blending properly (if you're using blending at all.)
For most applications, you'll probably want to use
gl.glEnable(gl.GL_BLEND);
gl.glBlendFunc(gl.GL_SRC_ALPHA,gl.GL_ONE_MINUS_SRC_ALPHA);
If neither of these things solve your problem, you might have to give us some more information about what you're doing/setting up prior to this section of your code.

If lighting is enabled, color comes from the material, not the glColor vertex colors. If your draw function that you mentioned is setting a material for the textured objects (and a white material under the texture would be common) then the rest of the cubes would be white. Using GL_COLOR_MATERIAL sets up OpenGL to take the glColor commands and update the material instead of just the vertex color, so that should work.
So, simply put, if you have lighting enabled, try GL_COLOR_MATERIAL.

One thing you might want to try is: glBindTexture(GL_TEXTURE_2D, 0); to bind the texture to nil.

Some things to check:
Is there a shader active?
Any gl-errors?
What other states did you change? For example GL_COLOR_MATERIAL, blending or lighting will change the appearance of your geometry.
Does it work if you draw the non-textured cube first? And if it does try to figure out at which point it turns white. It's also possible that the cube will only show up in the correct color in the first frame, then there's definitely a GL state involved.
Placing glPushAttrib/glPopAttrib at the beginning/end of your drawing methods might help, but it's better to figure out what caused the problem in the first place.