Draw the basic Geometry Objects. Hanyang University

Transcription

1 Draw the basic Geometry Objects Hanyang University

2 VERTEX ATTRIBUTE AND GEOMETRIC PRIMITIVES

3 Vertex Vertex A point in 3D space, or a corner of geometric primitives such as triangles, polygons. Vertex attributes Vertex coordinate Composition of primitives Vertex color Normal vector Texture coordinate

4 Vertex coordinate glvertex*() The function that specifies coordinate values of a vertex. To draw something, vertices have to be listed between glbegen() and glend() calls.

5 Vertex coordinate OpenGL coordinate system 3D cartesian coordinate system The view volume is a cube whose coordinate has a range of [-1.0, 1.0]. If larger view volumes or frustum view volumes are needed, we have to do projection transformations. In 2D case, the objects are lied in z=0 plane.

6 Geometric primitives Primitives

7 Polygon construction rules Polygon construction rules All the vertices of the polygon must lie in a single plane. The polygon cannot twist or bend in space. the polygon s edges must not intersect, and the polygon must be convex. Triangles absolutely obey the rules.

8 Polygon construction rules Wrong case : twisted quad glbegin(gl_quads); glvertex2f(-0.5, -0.5); glvertex2f(0.5, 0.5); glend(); glvertex2f(-0.5, 0.5); glvertex2f(0.5, -0.5);

9 Example code (glut version) #include <GL/glut.h> int primitive[] = {GL_POINTS, GL_LINES, GL_LINE_STRIP, GL_LINE_LOOP, GL_POLYGON, GL_QUADS, GL_TRIANGLES; int index; void mydisplay(){ glclear(gl_color_buffer_bit); glbegin(primitive[index]); glvertex2f(-0.5, 0.0); glvertex2f( , ); glvertex2f(0.0, 0.5); glvertex2f(0.3536, ); glvertex2f(0.5, 0.0); glvertex2f(0.3536, ); glvertex2f(0.0, -0.5); glvertex2f( , ); glend(); glflush(); void mykeyboard(unsigned char key, int x, int y) { if (key == 'n' key == 'N') index++; else if (key == 'p' key == 'P') index--; if (index < 0) index = 6; if (index > 6) index = 0; glutpostredisplay(); int main(int argc, char** argv){ glutcreatewindow("primitives"); glutdisplayfunc(mydisplay); glutkeyboardfunc(mykeyboard); glutmainloop();

10 (glfw version2) #include <GL/glfw.h> int primitive[] = {GL_POINTS, GL_LINES, GL_LINE_STRIP, GL_LINE_LOOP, GL_POLYGON, GL_QUADS, GL_TRIANGLES; int index; void mydisplay(){ glclear(gl_color_buffer_bit); glbegin(primitive[index]); glvertex2f(-0.5, 0.0); glvertex2f( , ); glvertex2f(0.0, 0.5); glvertex2f(0.3536, ); glvertex2f(0.5, 0.0); glvertex2f(0.3536, ); glvertex2f(0.0, -0.5); glvertex2f( , ); glend(); glflush(); void mykeyboard(int key, int action) { // action==glfw_press or GLFW_RELEASE if (action==glfw_release) return ; // do nothing if (key == 'n' key == 'N') index++; else if (key == 'p' key == 'P') index--; if (index < 0) index = 6; if (index > 6) index = 0; int main(int argc, char** argv){ glfwinit(); int BPP=32; glfwopenwindow(800, 600, BPP/3, BPP/3, BPP/3, 1, 8, 1, GLFW_WINDOW) ; glfwsetwindowtitle("tutorial"); glfwsetkeycallback(mykeyboard); while(glfwgetwindowparam(glfw_opened)) { mydisplay(); glfwswapbuffers(); // Shut down GLFW glfwterminate(); return 1;

11 (glfw version3) void mykeyboard(glfwwindow * win, int key, int scancode, int action, int mods) { // action==glfw_press or GLFW_RELEASE if (action==glfw_release) return ; // do nothing #include <GL/glfw.h> int primitive[] = {GL_POINTS, GL_LINES, GL_LINE_STRIP, GL_LINE_LOOP, GL_POLYGON, GL_QUADS, GL_TRIANGLES; int index; if (key == 'n' key == 'N') index++; else if (key == 'p' key == 'P') index--; if (index < 0) index = 6; if (index > 6) index = 0; void mydisplay(){ glclear(gl_color_buffer_bit); glbegin(primitive[index]); glvertex2f(-0.5, 0.0); glvertex2f( , ); glvertex2f(0.0, 0.5); glvertex2f(0.3536, ); glvertex2f(0.5, 0.0); glvertex2f(0.3536, ); glvertex2f(0.0, -0.5); glvertex2f( , ); glend(); glflush(); int main(int argc, char** argv){ glfwinit(); GLFWwindow* window = glfwcreatewindow(800, 600, "OpenGL Tutorialal", NULL, NULL); glfwmakecontextcurrent(window); glfwsetkeycallback(window, mykeyboard); while (!glfwwindowshouldclose(window)) { mydisplay(); glfwswapbuffers(window); glfwpollevents(); // Shut down GLFW glfwterminate(); return 1;

12 (fltk version)

13 Why GLFW? GLUT is outdated, unmaintained, and lacks features, but is widely used in graphics classes GLFW is better than glut, but is also very minimal (compared to other fully-featured GUI toolkits such as Qt or.net) FLTK is good if you need GUI widgets such as buttons (, and is much simpler than Qt,.net) Only GLUT, GLFW, FLTK are allowed in this class

14 Compile (Linux): First install, glfw: sudo apt-get install libglfw3-dev Then: g++ example.cpp -lgl -lglfw I will assume that you know how to build an app! Compile (windows): Or install libfltk-dev and then: g++ example.cpp -lgl -lfltk -lfltk_gl Install visual studio (express or professional) 2010 Download windows binaries of glfw 3.x. Add source files to a project Add library files (glfw.lib, gl.lib) to linker settings Or use cmake (multi-platform: win, linux, apple) Download practice2.zip After installing cmake, glfw and compiler cmake. make Or open the resulting.sln file on a win machine. CMakeLists.txt # -*- mode: cmake; -*- project(example) add_executable(example "./example.cpp" ) target_link_libraries(example GL glfw)

15 Vertex color Setting the current drawing color Specify the color of each vertex The colors of lines or surfaces are interpolated between the colors specified for each vertex. glcolor*() void glcolor4f (GLfloat red, GLfloat green, GLfloat blue, GLfloat alpha); void glcolor3f (GLfloat red, GLfloat green, GLfloat blue); The range of channels Real number : [0.0, 1.0] Integer : [0, 255]

16 Example code vertex color #include <GL/glut.h> int primitive[] = {GL_POINTS, GL_LINES, GL_LINE_STRIP, GL_LINE_LOOP, GL_POLYGON, GL_QUADS, GL_TRIANGLES; int index; void mydisplay(){ glclear(gl_color_buffer_bit); glbegin(primitive[index]); glcolor3f(1.0, 0.0, 0.0); glvertex2f(-0.5, 0.0); glcolor3f(0.0, 1.0, 0.0); glvertex2f( , ); glcolor3f(0.0, 0.0, 1.0); glvertex2f(0.0, 0.5); glcolor3f(0.5, 0.5, 0.5); glvertex2f(0.3536, ); glcolor3f(1.0, 1.0, 0.0); glvertex2f(0.5, 0.0); glcolor3f(1.0, 0.0, 1.0); glvertex2f(0.3536, ); glcolor3f(0.0, 1.0, 1.0); glvertex2f(0.0, -0.5); glcolor3f(1.0, 1.0, 1.0); glvertex2f( , ); glend(); // red // green // blue // gray // yellow // magenta // cyan // white void mykeyboard(unsigned char key, int x, int y) { if (key == 'n' key == 'N') index++; else if (key == 'p' key == 'P') index--; if (index < 0) index = 6; if (index > 6) index = 0; glutpostredisplay(); int main(int argc, char** argv){ glutcreatewindow("primitives"); glutdisplayfunc(mydisplay); glutkeyboardfunc(mykeyboard); glutmainloop(); glflush();

17 Other attributes Surface normal vectors A normal vector must be specified for each vertex, not for a face. To approximate surfaces which are not flat with flat and polygonal section. glnormal*() Used for lighting, backface culling Texture coordinates Specify texture coordinates Texture coordinates are used to map texture images to geometric primitives. gltexcoord*()

18 How to port glut apps to glfw Merge specialkeys and keyboard functions GLUT uses two different functions for character keys and special keys, but glfw does not. Add handling for GLFW_RELEASE Remove glutpostredisplay(); Substitute GLUT with GLFW Rewrite the main function

19 Download practice2.zip for GLFW version

20 How to build (linux) Install dependencies sudo apt-get install libglfw3-dev cmake Build cmake. make Run./OgreFltk

21 How to build (windows) Download dependencies and tools (google) Cmake Glfw windows binaries Build Open cmd cd to the source directory Assuming glfw bin.win32 folder is inside the source directory cmake. start OgreFltk.sln

22 How to build (windows) This will open a visual studio window Build Run Set OgreFltk as a startup project (using right click on the OgreFltk project) Copy glfw.dll to the source directory Set the source directory as working directory Ctrl+ F5