Blending Problem !

[Jehan]

Hello !
I have a problem with the blending under lwjgl / opengl ...
I am using a beige background texture like this:


and I want to blend over a red texture like this:


When I do this blending on Gimp I get this:


But when I do this blending on opengl with GL11.glBlendFunc (GL11.GL_SRC_ALPHA, GL11.GL_ONE_MINUS_SRC_ALPHA);
I get this:


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 !

[KaiHH]

You are probably missing:

glEnable(GL_BLEND);

[Jehan]

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...

[KaiHH]

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

[Jehan]

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;
	}

[Jehan]

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;
	}

[Jehan]

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!

[Jehan]

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 !!