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            Shuffy

            不斷的學習,不斷的思考,才能不斷的進步.Let's do better together!
            posts - 102, comments - 43, trackbacks - 0, articles - 19

                 本文在9篇文章的基礎上,為立方體加入紋理映射的功能。

            Texture Mapping

            Texture Mapping in OpenGL is a fairly straightforward concept. Every texture is nothing but an image of some sort. Texture mapping is basically applying a texture to a surface. Textures can be 1D, 2D or even 3D. A 1D texture is an image with either a width or a height, not both. They are not very useful. 2D textures have both width and height and are very useful. 3D textures are called Volume textures and are used in medical imaging applications for viewing CAT, MRI, and other 3D scans. We will look at using 2D textures in OpenGL as they are the most widely used in 3D Graphics.

            Windows Bitmap Files

            Images in Windows are typically stored in bitmap files. These images can be used as textures that will be applied to OpenGL surfaces. But before use them for texture mapping applications we should convert them to an OpenGL format. So we essentially have to read a Windows Bitmap into an OpenGL image. We can use the Auxiliary library to do so. It takes care of all the trouble involved in performing this conversion. Once a texture map is read into memory, the individual elements are called texels, just like an image's individual elements are called pixels. We wouldn't be dealing with these texels as we would be using the Aux library routine auxDIBImageLoadA to perform the conversion for us. Also, we need to make sure that the image dimensions are a power of 2. OpenGL images that we are going to use as a texture must have dimensions of a power of 2. Thus 32X32, 64X64, 128X64 etc. are all valid image sizes to be used as texture maps.

            Defining 2D Textures

            To define a 2D texture image in OpenGL we call glTexImage2D (when we are not using Mipmapping).

            Mipmapping

            When texture mapping is used with animation scaling of images cause some visual artifacts. This can be avoided by generating textures of various sizes from a large original texture and letting OpenGL automatically switch between the textures of various sizes. This technique is called Mipmapping and the individual textures are called Mipmaps. We can use the function gluBuild2DMipMaps to construct a series of mipmaps.

            Texture Modes

            OpenGL defines three texturing modes for different types of rendering. The first is GL_MODULATE, which modulates the current lighting and color information with the texture image. GL_DECAL is the second mode which only uses the texture image. Color and Lighting information will not affect the texture's appearance. The last mode is GL_BLEND, in which the texture image is blended with the current texture color and the current lighting and color information.

            Texture Filters

            OpenGL uses texture filters to interpolate between the texture pixels. It provides two types of texture filters: the minification filter (GL_TEXTURE_MIN_FILTER) for polygons smaller than the texture image and the magnification filter (GL_TEXTURE_MAG_FILTER) for polygons that are larger than the texture image. We'll look at how we will use these later in the tutorial.

            Texture Coordinates

            Texture Coordinates associate a particular location in the texture image with vertices in a polygon. These coordinates determine how the texture is mapped onto the polygon. Texture coordinates lie between 0.0 and 1.0 in case of 2D textures.

            Texture Wrapping

            When texture coordinates go outside the range of 0.0 to 1.0, they are either clamped to the surface or repeated. This can be specified by setting the GL_TEXTURE_WRAP_* parameter appropriately, to either GL_CLAMP or GL_REPEAT.

            Texture Objects

            Texture objects are a way of loading and maintaining multiple textures in memory without loading them each time before they are used. They are an optimization feature introduced recently in OpenGL.

            1,CCY457OpenGLView類中加入下列變量,分別代表紋理環繞,紋理過濾,紋理模式的參數。

                GLdouble m_texWrap, m_texFilter, m_texMode;  
                
            //All Texture Names
                 GLuint m_Texture[3]; //保存紋理對象的名稱

             并在構造函數中加入:

            CCY457OpenGLView::CCY457OpenGLView()
            {
                m_xRot 
            = 0.0f;
                m_yRot 
            = 0.0f;
                m_texWrap 
            = GL_CLAMP;
                m_texMode 
            = GL_DECAL;
                m_texFilter 
            = GL_NEAREST;
            }

            2,加載紋理對象。

            //Texture Mapping Functions
            void CCY457OpenGLView::LoadGLTextures()
            {
                
            //Create Texture Names
                glGenTextures(3, m_Texture);
                LoadTexture(
            "Apple.bmp",0);
                LoadTexture(
            "Fauve.bmp",1);
                LoadTexture(
            "Flower.bmp",2);
            }
            void CCY457OpenGLView::LoadTexture (CString fileName, int texName)
            {
                
            //Load Texture
                AUX_RGBImageRec* m_texture;
                m_texture 
            = auxDIBImageLoad((const char*)fileName);
                
            if(!m_texture)
                {
                    MessageBox(
            "Picture could not be loaded");
                    exit(
            1);
                }
                glBindTexture(GL_TEXTURE_2D, m_Texture[texName]);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, m_texWrap);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, m_texWrap);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, m_texFilter);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, m_texFilter);
                glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, m_texMode);
                gluBuild2DMipmaps(GL_TEXTURE_2D, 
            3, m_texture->sizeX,m_texture->sizeY, GL_RGB, GL_UNSIGNED_BYTE, m_texture->data);
            }

             3,加入控制紋理映射效果的各個菜單項及其事件處理程序

            void CCY457OpenGLView::OnTexturewrapGlclamp() 
            {
                m_texWrap 
            = GL_CLAMP;
                LoadGLTextures();
                InvalidateRect(NULL,FALSE);    
            }
            void CCY457OpenGLView::OnUpdateTexturewrapGlclamp(CCmdUI* pCmdUI) 
            {
                
            if(m_texWrap == GL_CLAMP)
                    pCmdUI
            ->SetRadio();
                
            else
                    pCmdUI
            ->SetRadio(FALSE);    
            }
            void CCY457OpenGLView::OnTexturewrapGlrepeat() 
            {
                m_texWrap 
            = GL_REPEAT;
                LoadGLTextures();
                InvalidateRect(NULL,FALSE);
            }
            void CCY457OpenGLView::OnUpdateTexturewrapGlrepeat(CCmdUI* pCmdUI) 
            {
                
            if(m_texWrap == GL_REPEAT)
                    pCmdUI
            ->SetRadio();        
                
            else
                    pCmdUI
            ->SetRadio(FALSE);
            }
            void CCY457OpenGLView::OnTexturefilterGlnearest() 
            {
                m_texFilter 
            = GL_NEAREST;
                LoadGLTextures();
                InvalidateRect(NULL,FALSE);        
                
            }
            void CCY457OpenGLView::OnUpdateTexturefilterGlnearest(CCmdUI* pCmdUI) 
            {
                
            if(m_texFilter == GL_NEAREST)
                    pCmdUI
            ->SetRadio();    
                
            else
                    pCmdUI
            ->SetRadio(FALSE);    
            }
            void CCY457OpenGLView::OnTexturefilterGllinear() 
            {
                m_texFilter 
            = GL_LINEAR;
                LoadGLTextures();
                InvalidateRect(NULL,FALSE);        
            }
            void CCY457OpenGLView::OnUpdateTexturefilterGllinear(CCmdUI* pCmdUI) 
            {
                
            if(m_texFilter == GL_LINEAR)
                    pCmdUI
            ->SetRadio();    
                
            else
                    pCmdUI
            ->SetRadio(FALSE);    
            }
            void CCY457OpenGLView::OnTexturemodeGlmodulate() 
            {
                m_texMode 
            = GL_MODULATE;
                LoadGLTextures();
                InvalidateRect(NULL,FALSE);
            }
            void CCY457OpenGLView::OnUpdateTexturemodeGlmodulate(CCmdUI* pCmdUI) 
            {
                
            if(m_texMode == GL_MODULATE)
                    pCmdUI
            ->SetRadio();                
                
            else
                    pCmdUI
            ->SetRadio(FALSE);    
            }
            void CCY457OpenGLView::OnTexturemodeGldecal() 
            {
                m_texMode 
            = GL_DECAL;
                LoadGLTextures();
                InvalidateRect(NULL,FALSE);
            }
            void CCY457OpenGLView::OnUpdateTexturemodeGldecal(CCmdUI* pCmdUI) 
            {
                
            if(m_texMode == GL_DECAL)
                    pCmdUI
            ->SetRadio();                
                
            else
                    pCmdUI
            ->SetRadio(FALSE);
            }
            void CCY457OpenGLView::OnTexturemodeGlblend() 
            {
                m_texMode 
            = GL_BLEND;
                LoadGLTextures();
                InvalidateRect(NULL,FALSE);
            }
            void CCY457OpenGLView::OnUpdateTexturemodeGlblend(CCmdUI* pCmdUI) 
            {
                
            if(m_texMode == GL_BLEND)
                    pCmdUI
            ->SetRadio();                
                
            else
                    pCmdUI
            ->SetRadio(FALSE);
            }

            4,在InitializeOpenGL()中加入如下調用:

                //加載紋理
                LoadGLTextures();

            5,繪制函數修改如下:

            void CCY457OpenGLView::RenderScene ()
            {
            //繪制函數
                    glTranslatef(0.0f,0.0f,-5.0f);
                    glRotatef(m_xRot,
            1.0f,0.0f,0.0f);
                    glRotatef(m_yRot,
            0.0f,1.0f,0.0f);
                    glEnable(GL_TEXTURE_2D);
                    glBindTexture(GL_TEXTURE_2D,m_Texture[
            0]);
                    
            //Front Face
                    glBegin(GL_POLYGON);
                        glTexCoord2f(
            0,0);
                        glVertex3f(
            -1.0f,-1.0f,0.0f);
                        glTexCoord2f(
            1,0);
                        glVertex3f( 
            1.0f,-1.0f,0.0f);
                        glTexCoord2f(
            1,1);
                        glVertex3f( 
            1.0f1.0f,0.0f);
                        glTexCoord2f(
            0,1);
                        glVertex3f(
            -1.0f1.0f,0.0f);
                    glEnd();
                    
            //Back Face
                    glBegin(GL_POLYGON);
                        glTexCoord2f(
            1,0);
                        glVertex3f(
            -1.0f,-1.0f,-1.0f);
                        glTexCoord2f(
            1,1);
                        glVertex3f(
            -1.0f1.0f,-1.0f);
                        glTexCoord2f(
            0,1);
                        glVertex3f( 
            1.0f1.0f,-1.0f);
                        glTexCoord2f(
            0,0);
                        glVertex3f( 
            1.0f,-1.0f,-1.0f);
                    glEnd();
                    glBindTexture(GL_TEXTURE_2D,m_Texture[
            1]);
                    
            //Left Face
                    glBegin(GL_POLYGON);
                        glTexCoord2f(
            1,0);
                        glVertex3f(
            -1.0f,-1.0f0.0f);
                        glTexCoord2f(
            1,1);
                        glVertex3f(
            -1.0f1.0f0.0f);
                        glTexCoord2f(
            0,1);
                        glVertex3f(
            -1.0f1.0f,-1.0f);
                        glTexCoord2f(
            0,0);
                        glVertex3f(
            -1.0f,-1.0f,-1.0f);
                    glEnd();
                    
            //Right Face
                    glBegin(GL_POLYGON);
                        glTexCoord2f(
            0,0);
                        glVertex3f(
            1.0f,-1.0f0.0f);
                        glTexCoord2f(
            1,0);
                        glVertex3f(
            1.0f,-1.0f,-1.0f);
                        glTexCoord2f(
            1,1);
                        glVertex3f(
            1.0f1.0f,-1.0f);
                        glTexCoord2f(
            0,1);
                        glVertex3f(
            1.0f1.0f0.0f);
                    glEnd();
                    glBindTexture(GL_TEXTURE_2D,m_Texture[
            2]);
                    
            //Top Face
                    glBegin(GL_POLYGON);
                        glTexCoord2f(
            0,0);
                        glVertex3f(
            -1.0f1.0f,  0.0f);
                        glTexCoord2f(
            0,1);
                        glVertex3f( 
            1.0f1.0f,  0.0f);
                        glTexCoord2f(
            1,1);
                        glVertex3f( 
            1.0f1.0f-1.0f);
                        glTexCoord2f(
            1,0);
                        glVertex3f(
            -1.0f1.0f-1.0f);
                    glEnd();
                    
            //Botton Face
                    glBegin(GL_POLYGON);
                        glTexCoord2f(
            0,1);
                        glVertex3f(
            -1.0f-1.0f,  0.0f);
                        glTexCoord2f(
            0,0);
                        glVertex3f(
            -1.0f-1.0f-1.0f);
                        glTexCoord2f(
            1,0);
                        glVertex3f( 
            1.0f-1.0f-1.0f);
                        glTexCoord2f(
            1,1);
                        glVertex3f( 
            1.0f-1.0f,  0.0f);
                    glEnd();
                    glDisable(GL_TEXTURE_2D);
            }

             

             

            作者:洞庭散人

            出處:http://phinecos.cnblogs.com/    

            本文版權歸作者和博客園共有,歡迎轉載,但未經作者同意必須保留此段聲明,且在文章頁面明顯位置給出原文連接,否則保留追究法律責任的權利。
            原文鏈接:http://www.cnblogs.com/phinecos/archive/2008/11/05/1327646.html
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