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texture coordinate to texel

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Hello, I have a texture atlas for an object in my scene. If i search the pixel in my texture that corresponds to my texture coordinate and i change its color, i get a strange result. While in my texture only one pixel is change from color, i get after texture mapping more changes. Here is the link to the screenshots of my problem, that makes my problem more clearly. void Texture::adjust(const Vector2D& texcoord, const Vector3D& color, float alpha) { float u=texcoord.getU(); float v=texcoord.getV(); float x = (u-floorf(u))*m_width; float y = (v-floorf(v))*m_height; float i = floorf(x); float j = floorf(y); unsigned char* pix=lookup_raw((int)i,(int)j); pix[0]=(unsigned char)(color.getR()<0.f ? 0.f: color.getR()>1.f ? 255.f : color.getR()*255.f); pix[1]=(unsigned char)(color.getG()<0.f ? 0.f: color.getG()>1.f ? 255.f : color.getG()*255.f); pix[2]=(unsigned char)(color.getB()<0.f ? 0.f: color.getB()>1.f ? 255.f : color.getB()*255.f); if(m_channels==4) pix[3]=(unsigned char)(alpha<0.f ? 0.f: alpha>1.f ? 255.f : alpha*255.f); } inline unsigned char* Texture::lookup_raw(int col, int row) { return m_map + m_channels * (m_width*row + col); }

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