Draw a Simple Object

Pixel pipeline Vertex pipeline Course Map Transformation & Lighting Primitive assembly Viewport culling & clipping Texture blending Per Fragment operations Buffer operations Rasterizer setup Framebuffer We are here!

Example 1/4 #include “ glut.h ” void display(); void reshape(GLsizei w, GLsizei h); void main(int argc, char** argv){ glutInit(&argc, argv); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); glutInitWindowSize(250, 250); glutInitWindowPosition(100, 100); glutCreateWindow("Drawing sample"); glutDisplayFunc(display); glutReshapeFunc(reshape); glutMainLoop(); }

Example 2/4 void reshape(GLsizei w, GLsizei h){ glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(-2.0, 2.0, -2.0, 2.0, -2.0, 2.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); }

Example 3/4 void display(){ glClearColor(0.0f, 0.0f, 0.0f, 0.0f); glClear(GL_COLOR_BUFFER_BIT); glBegin(GL_POLYGON); glColor3f(1.0f, 1.0f, 1.0f); glVertex3f(-1.0f, -1.0f, 0.0f); glColor3f(1.0f, 0.0f, 0.0f); glVertex3f(1.0f, -1.0f, 0.0f); glColor3f(0.0f, 1.0f, 0.0f); glVertex3f(1.0f, 1.0f, 0.0f); glColor3f(0.0f, 0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, 0.0f); glEnd(); glFlush(); }

Example 4/4

Data Type

Clear the buffers 1/2 void glClearColor(GLclampf, GLclampf, GLclampf, GLclampf ) Set the current values for use in cleaning color buffers in RGBA mode. void glClearDepth(GLclampd) Set the current values for use in cleaning depth buffer.

Clear the buffers 2/2 void glClear(GLbitfield) Clear the specified buffers to their current clearing values. GL_COLOR_BUFFER_BIT GL_DEPTH_BUFFER_BIT GL_ACCUM_BUFFER_BIT GL_STENCIL_BUFFER_BIT

Color representation RGBA: red, green, blue, alpha Each channel has intensity from 0.0~1.0 Values outside this interval will be clamp to 0.0 or 1.0 Alpha is used in blending and transparency Specify a color: glColor{34}{sifd}[v]( … )

Points, Lines and Polygons 1/4 Describe points, lines, polygons void glBegin(GLenum) Marks the beginning of a vertex-data list The mode can be any of the values in next page void glEnd() Marks the end of a vertex-data list

Points, Lines and Polygons 2/4

Points, Lines and Polygons 3/4

Points, Lines and Polygons 4/4 Specifying the vertices glVertex{234}{sifd}[v]( … ) Specifies a vertex for use in describing a geometric object Can only effective between a glBegin() and glEnd() pair

Completion of Drawing void glFlush() Forces previously issued OpenGL commands to begin execution. void glFinish() Forces previous issued OpenGL commands to complete. void glutSwapBuffers() Swap front and back buffers.

See also Display List Store the OpenGL commands Vertex Array + Vertex Buffer Object Store the vertices data in VGA memory