Problem with alpha channel shader

[jimy-byerley]

It is probably a stupid problem of beginners ...
I'm trying to make a cloud system with random placement of square faces, each face have a random cloud texture.
I heard the integrated billboard class in irrlicht was too slow with a big number of objects, so I written a small vertex shader.

I have to use EMT_TRANSPARENT_ALPHA_CHANNEL material to construct my HightLevelMaterial.
But instead of drawing a blended face It give me an opaque face. Only the absolutly transparent (alpha=0.000000) pixels are transparent.

I tried some other tricks, like using EMT_ONETEXTURE_BLEND instead, setting manually material.MaterialTypeParam:

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material.MaterialTypeParam = video::pack_textureBlendFunc(video::EBF_SRC_ALPHA, video::EBF_ONE_MINUS_SRC_ALPHA,
                                                    video::EMFN_MODULATE_1X, video::EAS_TEXTURE | video::EAS_VERTEX_COLOR); 

I'm also using a custom SceneNode that draw itself a simple square.

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class FaceNode : public scene::ISceneNode
{
    core::aabbox3d<f32> Box;
    video::S3DVertex Vertices[4];
    video::SMaterial Material;
public:
 
    FaceNode(scene::ISceneNode* parent, scene::ISceneManager* mgr) 
    : scene::ISceneNode(parent, mgr)
    {
        //Material.Wireframe = false;
        // S3DVertex (f32 x, f32 y, f32 z, f32 nx, f32 ny, f32 nz, SColor c, f32 tu, f32 tv)
        Vertices[0] = video::S3DVertex( 0,0,0,  0,0,-1, video::SColor(0,0,0,0), 0, 0);
        Vertices[1] = video::S3DVertex( 0,1,0,  0,0,-1, video::SColor(0,0,0,0), 1, 0);
        Vertices[2] = video::S3DVertex( 1,0,0,  0,0,-1, video::SColor(0,0,0,0), 0, 1);
        Vertices[3] = video::S3DVertex( 1,1,0,  0,0,-1, video::SColor(0,0,0,0), 1, 1);
        Box.reset(Vertices[0].Pos);
        for (s32 i=1; i<4; ++i)
            Box.addInternalPoint(Vertices[i].Pos);
    }
    virtual void OnRegisterSceneNode()
    {
        if (IsVisible)
            SceneManager->registerNodeForRendering(this);
        ISceneNode::OnRegisterSceneNode();
    }
    virtual void render()
    {
        u16 indices[] = {0,1,3,   0,3,2}; // order of indices of points decide the normal of the plane
        video::IVideoDriver* driver = SceneManager->getVideoDriver();
 
        driver->setMaterial(Material);
        driver->setTransform(video::ETS_WORLD, AbsoluteTransformation);
        driver->drawVertexPrimitiveList(&Vertices[0], 4, &indices[0], 4, video::EVT_STANDARD, scene::EPT_TRIANGLES, video::EIT_16BIT);
    }
    virtual const core::aabbox3d<f32>& getBoundingBox() const
    { return Box; }
 
    virtual u32 getMaterialCount() const
    { return 1; }
 
    virtual video::SMaterial& getMaterial(u32 i)
    { return Material; }   
};

I load my shader as it

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        s32 matnum;
        if (bCanDoGLSL_1_1)
        {
            matnum = gpu->addHighLevelShaderMaterialFromFiles(
                "cloud.vert", "main", video::EVST_VS_1_1,
                "cloud.frag", "main", video::EPST_PS_1_1,
                0, video::EMT_TRANSPARENT_ALPHA_CHANNEL);
            node->setMaterialType((video::E_MATERIAL_TYPE)matnum);
        }
        else
            printf("no opengl support\n");
        
        video::SMaterial material = node->getMaterial(0);
        material.Lighting = false;
        //material.MaterialType = video::EMT_TRANSPARENT_ALPHA_CHANNEL;
        material.MaterialTypeParam = video::pack_textureBlendFunc(video::EBF_SRC_ALPHA, video::EBF_ONE_MINUS_SRC_ALPHA,
                                                    video::EMFN_MODULATE_1X, video::EAS_TEXTURE | video::EAS_VERTEX_COLOR); 
        // this is not working
        // material.BackfaceCulling = false;
        node->setMaterialFlag(video::EMF_BACK_FACE_CULLING, false); 
        material.setTexture(0, driver->getTexture("cloud-2.png"));
 

I don't know if it can be usefull: I work on Debian Jessie (8) with an NVIDIA GT520, I got Irrlicht 1.8.1.

SOLUTION FOUND !
I just added the following line after the shader assignation. It now works as expected.

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node->setMaterialFlag(video::EMF_BLEND_OPERATION, true);

[mongoose7]

EMT_TRANSPARENT_ALPHA_CHANNEL works. Maybe you have a problem in your pixel shader.

[jimy-byerley]

I'm not sure but I don't know: when I force gl_FragColor alpha to 0.5, only one thing change: there is no more alpha even in texture transparent zones (100% transparence zones). It's logical because 0.5 is always > 0 (my name's captain obvious ?)

Anyway, this is my vertex shader

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varying vec4 vertex;
 
void main()
{
    // for the fragment
    gl_TexCoord[0].st = gl_MultiTexCoord0;
    vertex = gl_ModelViewMatrix * gl_Vertex;
    // the model view matrix (from world to screen) have a translation transform and a rotation transform.
    // the rotation transform is the mat3 of the center: columns 0, 1, 2 and lines 0, 1, 2
    // to abort rotation of the object in view, we set this matrix to identity matrix.
    mat4 ModelView = gl_ModelViewMatrix;
    // matrix[col][lin]
    ModelView[0][0] = 1;
    ModelView[0][1] = 0;
    ModelView[0][2] = 0;
    
    ModelView[1][0] = 0;
    ModelView[1][1] = 1;
    ModelView[1][2] = 0;
    
    ModelView[2][0] = 0;
    ModelView[2][1] = 0;
    ModelView[2][2] = 1;
    gl_Position = gl_ProjectionMatrix * ModelView * gl_Vertex;
 

And this is my fragment shader

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sampler2D texture;
varying vec4 vertex;
 
#define NUM_LIGHTS 3 //gl_MaxLights
 
void main()
{
    float color = texture2D(texture, gl_TexCoord[0].st).r;
    vec3 light = 0;
    vec4 lv;
    int i=0;
    for (i; i<NUM_LIGHTS; i++)
    {
        lv = gl_LightSource[i].position - vertex;
        light += gl_LightSource[i].diffuse / pow(length(lv), 2);
    }
    light = 0.05 + 0.2*light;
    gl_FragColor = vec4(light*color, color);
}
 

[hendu]

You sure you want the red channel as alpha?

[mongoose7]

They are clouds so they should be mostly white. But I think he should disable the depth test.

[jimy-byerley]

Exactly, my clouds are only white, the only value I need is the transparency stored on r channel (I use grayscale images).
I tried to disable the depth test by:

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node->setMaterialFlag(video::EMF_ZBUFFER, false); 

But it doesn't change anything. Anyway I need depth test for clouds.

[jimy-byerley]

Someone have something for me ?

[mongoose7]

Post an image. Two clouds and background.

[jimy-byerley]

What I get with 2 cloud faces. The color gradient on the second is normal because it's near a light point.

[hendu]

According to that image, your shader isn't applied? There are black areas with red = 0. Confirm by checking the source image's alpha channel.

[jimy-byerley]

My shader is applied : There is the billboard effect and the color gradient near lights.
In fact black zones we see is not absolutly black zones, The texture is at 100% black only in the transparent area.
let's see the image

[mongoose7]

And how do you account for the irregular shapes of the textures in the compound image you posted?

[hendu]

If you run example 10, does it show ok?

[jimy-byerley]

And how do you account for the irregular shapes of the textures in the compound image you posted?

The irregular shape is due to non zero pixels in the image, maybe because of the jpeg compression (the image was in jpg before I converted it into png).

If you run example 10, does it show ok?

It works fine, yes ... I'll try find the difference between this code and mine ...

[jimy-byerley]

I FOUND !!!

In addition to build the shader on EMT_TRANSPARENT_ALPHA_CHANNEL, we have to declare the blend operation :

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node->setMaterialFlag(video::EMF_BLEND_OPERATION, true);

And I don't think it was often said in the documentation !
Thanks for all your answers, my result is now: