绘制纹理贴图是缺个角，怎么办？

glBindTexture(GL_TEXTURE_2D, 0);
glViewport(2*w/3, 0, w/3, h);
glLoadIdentity();
glEnable(GL_TEXTURE_2D);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
glBindTexture(GL_TEXTURE_2D, texName2);
glBegin(GL_QUADS);
glTexCoord2f(0.0f, 0.0f);//设置当前纹理坐标(第四步)
glVertex2f(-1.0f, 1.0f);
glTexCoord2f(1.0f, 0.0f);//设置当前纹理坐标(第四步)
glVertex2f(1.0f, 1.0f);
glTexCoord2f(0.0f, 1.0f);//设置当前纹理坐标(第四步)
glVertex2f(-1.0f, -1.0f);
glTexCoord2f(1.0f, 1.0f);//设置当前纹理坐标(第四步)
glVertex2f(1.0f, -1.0f);
glEnd();
glFlush();
glDisable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, 0);

搞定要按顺序