OpenGL: OpenGL下实现图片满屏显示

实现图片满屏显示，最常用的用途是把一张图片作为显示窗体的背景图片。我这里有总两种方法：

 一、 正交模式显示背景图片

1. 关闭深度测试
2. 正交投影
3. 设置四边形的尺寸为窗口四个角，将图片贴到Quad上
4. 切换到透视模式下
5. 开启深度测试
6. 显示三维场景

绘制背景图片时必须关闭深度测试，否则会导致后面渲染的3d场景不能显示。 

在绘制3d场景时开启深度测试是为了保证3D模型绘制的正确性，主要指彼此的遮挡关系。

示例代码：

void display(void){    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );    glColor3f (1.0, 1.0, 1.0);    glDisable(GL_DEPTH_TEST);// 切换到正交模式    glMatrixMode(GL_PROJECTION);      glLoadIdentity();      glOrtho(0, g_fWidth, 0, g_fHeight, 0, g_fDepth);      glMatrixMode(GL_MODELVIEW);      glLoadIdentity();  glDisable(GL_LIGHTING);glEnable(GL_TEXTURE_2D);glBindTexture( GL_TEXTURE_2D, g_textureID ); glInterleavedArrays( GL_T2F_V3F, 0, g_bgVertices ); glDrawArrays( GL_QUADS, 0, 4 );// 绘制背景图片glEnable(GL_LIGHTING);glDisable(GL_TEXTURE_2D);    //  切换到三维场景    glMatrixMode (GL_PROJECTION);       //回复原有的设置      glLoadIdentity ();  gluPerspective(30, g_fWidth/g_fHeight, 0.001, 100.0);glMatrixMode(GL_MODELVIEW);    glLoadIdentity ();             gluLookAt(0, 5, 5, 0, 0, 0, 0, 1, 0);glEnable(GL_DEPTH_TEST);glPushMatrix();{glTranslatef(0, 0, 0);glRotatef(g_xAngle, 1, 0, 0);glRotatef(g_yAngle, 0, 1, 0);glCallList(g_modelId);// 绘制三维图形} glPopMatrix();glFlush();// glutPostRedisplay();}

二、 透视模式显示背景图片

背景图片和3d场景都在透视模式下显示，此时为了精确实现图片满屏，需要将窗口四个角的坐标投影到3d场景中，计算出对应的四边形四个角坐标，然后图片贴上去。步骤如下：

1. 窗口四角 投影到3d场景中，使用gluUnProject函数 计算出新的quad
2. 关闭深度测试
3. 绘制quad，贴图
4. 开启深度测试
5. 绘制3d场景

示例代码：

void display(void){    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );    glColor3f (1.0, 1.0, 1.0);  ComputeBackgroundQuad();glDisable(GL_DEPTH_TEST);// 绘制背景图片glDisable(GL_LIGHTING);glEnable(GL_TEXTURE_2D);glBindTexture( GL_TEXTURE_2D, g_textureID );glEnableClientState( GL_VERTEX_ARRAY );glEnableClientState( GL_TEXTURE_COORD_ARRAY ); glInterleavedArrays( GL_T2F_V3F, 0, g_bgVertices ); glDrawArrays( GL_QUADS, 0, 4 );glDisableClientState( GL_VERTEX_ARRAY );glDisableClientState( GL_TEXTURE_COORD_ARRAY );glDisable(GL_TEXTURE_2D);glEnable(GL_LIGHTING);glEnable(GL_DEPTH_TEST);glPushMatrix();{glTranslatef(0, 0, g_fOffset);glRotatef(g_xAngle, 1, 0, 0);glRotatef(g_yAngle, 0, 1, 0);glCallList(g_modelId);} glPopMatrix();glFlush();// glutPostRedisplay();}

void ComputeBackgroundQuad(){GLintviewport[4];GLdouble projMatrix[16];GLdouble modelMatrix[16];// glGetDoublev(GL_PROJECTION, projMatrix);  缺少matrix但是编译不报错~glGetDoublev(GL_PROJECTION_MATRIX, projMatrix);glGetDoublev(GL_MODELVIEW_MATRIX, modelMatrix);glGetIntegerv(GL_VIEWPORT, viewport);// double objX, objY, objZ;const double winZ = 0;  // 0 / 1gluUnProject(0, 0, winZ, modelMatrix, projMatrix, viewport, &objX, &objY, &objZ);g_bgVertices[0].x = objX;g_bgVertices[0].y = objY;g_bgVertices[0].z = objZ;gluUnProject(g_fWidth, 0, winZ, modelMatrix, projMatrix, viewport, &objX, &objY, &objZ);g_bgVertices[1].x = objX;g_bgVertices[1].y = objY;g_bgVertices[1].z = objZ;gluUnProject(g_fWidth, g_fHeight, winZ, modelMatrix, projMatrix, viewport, &objX, &objY, &objZ);g_bgVertices[2].x = objX;g_bgVertices[2].y = objY;g_bgVertices[2].z = objZ;gluUnProject(0, g_fHeight, winZ, modelMatrix, projMatrix, viewport, &objX, &objY, &objZ);g_bgVertices[3].x = objX;g_bgVertices[3].y = objY;g_bgVertices[3].z = objZ;}

最终的效果如图：

http://blog.csdn.net/ryfdizuo/article/details/7596242