LWJGL Forum

Hello !
I have a problem with the blending under lwjgl / opengl ...
I am using a beige background texture like this:
(https://i.ibb.co/mR6J89x/beige.png)

and I want to blend over a red texture like this:
(https://i.ibb.co/fdnD6vD/test7.png)

When I do this blending on Gimp I get this:
(https://i.ibb.co/kKQCNL2/test6.png)

But when I do this blending on opengl with GL11.glBlendFunc (GL11.GL_SRC_ALPHA, GL11.GL_ONE_MINUS_SRC_ALPHA);
I get this:
(https://i.ibb.co/ZS8mG5j/test8.png)

There is indeed transparency, but it is too much opaque.
When I check the RGB value of the resulting pixels under GIMP, I got: resultColor = (srcAlpha * srcColor + (1 - srcAlpha) * dstColor). it works !
But with opengl, the equation is not respected, the transparency is much more opaque than it should be.

My fragment shader is quite standard, I only sample the texture:
vec4 textureColour = texture (modelTexture, pass_textureCoordinates);
out_Color = textureColour;


I don't understand where the problem is coming from, would anyone know?

Thankyou for answers !

You are probably missing:

glEnable(GL_BLEND);


Hi thankyou for answer,

no, I have enabled gl Blend for sure:

GL11.glEnable (GL11.GL_BLEND);
GL11.glBlendFunc (GL11.GL_SRC_ALPHA, GL11.GL_ONE_MINUS_SRC_ALPHA);
GL11.glDepthMask (false);

// drawing

GL11.glDepthMask (true);
GL11.glDisable (GL11.GL_BLEND);

like that

transparency works, but what appears to be transparent is much more opaque than expected, but still transparent...
(https://i.ibb.co/sRFJMQZ/test9.png)

Then the problem is in how you load the texture.
Do you have a minimal, complete and verifiable example program that reproduces the problem?

I have several texture load functions, I have tried all of them and get the same result, I think they are quite similar to each other.

Here is one:

import org.newdawn.slick.opengl.Texture;
import org.newdawn.slick.opengl.TextureLoader;

public int loadTextureEssai(String fileName)
{
Texture texture = null;
try {
texture = TextureLoader.getTexture("PNG", Class.class.getResourceAsStream("/res/" + fileName + ".png"));
GL30.glGenerateMipmap(GL11.GL_TEXTURE_2D);
GL11.glTexParameteri(GL11.GL_TEXTURE_2D, GL11.GL_TEXTURE_MAG_FILTER, GL11.GL_LINEAR_MIPMAP_LINEAR);
GL11.glTexParameteri(GL11.GL_TEXTURE_2D, GL11.GL_TEXTURE_MIN_FILTER, GL11.GL_LINEAR_MIPMAP_LINEAR);
GL11.glTexParameteri(GL11.GL_TEXTURE_2D, GL11.GL_TEXTURE_WRAP_S, GL12.GL_CLAMP_TO_EDGE);
GL11.glTexParameteri(GL11.GL_TEXTURE_2D, GL11.GL_TEXTURE_WRAP_T, GL12.GL_CLAMP_TO_EDGE);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
int textureID = texture.getTextureID();
textures.add(textureID);
return textureID;
}

here is another one:

import de.matthiasmann.twl.utils.PNGDecoder;
import de.matthiasmann.twl.utils.PNGDecoder.Format;


public int loadTexture1(String fileName)
{
int width = 0;
int height = 0;
ByteBuffer buffer = null;
try {
InputStream in = Class.class.getResourceAsStream("/res/" + fileName + ".png");
PNGDecoder decoder = new PNGDecoder(in);
width = decoder.getWidth();
height = decoder.getHeight();
buffer = ByteBuffer.allocateDirect(4 * width * height);
decoder.decode(buffer, width * 4, Format.BGRA);
buffer.flip();
in.close();
} catch (Exception e) {
e.printStackTrace();
System.err.println("Tried to load texture " + fileName + ", didn't work");
System.exit(-1);
}
TextureData currentTextureData = new TextureData(buffer, width, height);

int id = loadTexture2(currentTextureData);

textures.add(id);

return id;
}

protected static int loadTexture2(TextureData data)
{
int texID = GL11.glGenTextures();
GL13.glActiveTexture(GL13.GL_TEXTURE0);
GL11.glBindTexture(GL11.GL_TEXTURE_2D, texID);
GL11.glPixelStorei(GL11.GL_UNPACK_ALIGNMENT, 1);
GL11.glTexImage2D(GL11.GL_TEXTURE_2D, 0, GL11.GL_RGBA, data.getWidth(), data.getHeight(), 0, GL12.GL_BGRA,
GL11.GL_UNSIGNED_BYTE, data.getBuffer());

GL30.glGenerateMipmap(GL11.GL_TEXTURE_2D);
GL11.glTexParameteri(GL11.GL_TEXTURE_2D, GL11.GL_TEXTURE_MAG_FILTER, GL11.GL_LINEAR_MIPMAP_LINEAR);
GL11.glTexParameteri(GL11.GL_TEXTURE_2D, GL11.GL_TEXTURE_MIN_FILTER, GL11.GL_LINEAR_MIPMAP_LINEAR);
GL11.glTexParameterf(GL11.GL_TEXTURE_2D, GL14.GL_TEXTURE_LOD_BIAS, 0.0f);
if (GLContext.getCapabilities().GL_EXT_texture_filter_anisotropic)
{
float amount = Math.min(4f, GL11.glGetFloat(EXTTextureFilterAnisotropic.GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT));
GL11.glTexParameterf(GL11.GL_TEXTURE_2D, EXTTextureFilterAnisotropic.GL_TEXTURE_MAX_ANISOTROPY_EXT, amount);
}
else
{
System.out.println("Not supported");
}
GL11.glBindTexture(GL11.GL_TEXTURE_2D, 0);
return texID;
}

ok, i did a minimal program, but it works!

Now I have to compare the two programs, see where my mistake was!

Thanks for the coaching, KaiHH!

Ok, I found my mistake, I had displayed the red spot on itself several times without wanting to.

I apologize for wasting your time, thank you !!