Question

I am trying to display a texture on a square using opengl es 1 using the ndk.
I am using this “hacks” to load a png from the apk : http://www.anddev.org/ndk_opengl_-_loading_resources_and_assets_from_native_code-t11978.html

This seems to work fine.
When i want to apply the texture to my quad, the texture seems to be duplicate.

After some research i think the problem is coming from my rendering code :

//the order is correct even if it is not in the numeric order
GLfloat vertexBuffer[] = {
    _vertices[0].x, _vertices[0].y,
    _vertices[3].x, _vertices[3].y,
    _vertices[1].x, _vertices[1].y,
    _vertices[2].x, _vertices[2].y,
};

GLfloat texCoords[] = {
    0.0, 1.0, //  left-bottom 
    1.0, 1.0, //  right-bottom
    0.0, 0.0, //  left-top
    1.0, 0.0 //  right-top
};

glBindTexture(GL_TEXTURE_2D, _texture->getTexture());
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glTexCoordPointer(2, GL_FLOAT, 0, texCoords); 
glVertexPointer(2, GL_FLOAT, 0, vertexBuffer);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glBindTexture(GL_TEXTURE_2D, 0);

Answer 1

The problem was definitly is the png loading function.
I add a test to check if the image contain an alpha channel using the libpng :

bool hasAlpha;
switch (info_ptr->color_type) {
    case PNG_COLOR_TYPE_RGBA:
        hasAlpha = true;
        break;
    case PNG_COLOR_TYPE_RGB:
        hasAlpha = false;
        break;
    default:
        png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
        zip_fclose(file);
        return TEXTURE_LOAD_ERROR;
}

And i changed the glTexImage2D parameters “internalformat” and “format”:

glTexImage2D(GL_TEXTURE_2D, 0, hasAlpha ? GL_RGBA : GL_RGB, width, height, 0, hasAlpha ? GL_RGBA : GL_RGB, GL_UNSIGNED_BYTE, (GLvoid*) image_data);