Comp2.pdf

IT2202 Pygame and OpenGL Every shader must contain a main() function. The...

IT2202 Pygame and OpenGL Every shader must contain a main() function. The void keyword indicates Windows, Points, and Shapes that no values are returned, and the main function requires no parameters. Based on the graphics pipeline, the first step to render graphics is to develop Vertex shaders manipulate coordinates in a 3D space and are called once per an application where the graphics will be displayed. vertex. The purpose of the vertex shader is to set up the gl_Position variable, a special, global, and built-in GLSL variable. It is used to store the A window is a graphical interface element that displays an application’s position of the current vertex. content. Below are the phases of an interactive and graphics-based windowed application. GLSL has vector data types, which are often used for storing values that 1. Startup: During this stage, objects are created, values are initialized, indicate positions, colors, and texture coordinates. Vectors may have two, and any required external files are loaded. three, or four components, indicated by vec2, vec3, and vec4 (for vectors 2. Main Loop: This stage repeats continuously while the application is consisting of floats). The four (4) float values represent the vertex's x, y, z, and running. It consists of the following three (3) substages: w positions. The fourth parameter (w) is used to manipulate the clipping of the o Process Input – checks if the user has performed any action that vertex position in the 3D space. Its default value is 1.0. sends data to the computer, such as pressing keys on a keyboard or clicking buttons on a mouse. Every vertex shader that you write will use arrays of data stored in vertex o Update – changes values of variables and objects. buffers. Multiple points are needed to specify the shapes of two-dimensional o Render – creates graphics that are displayed on the screen. or three-dimensional objects. Below is a sample code to draw a 3D triangle. 3. Shutdown: This stage typically begins when the user performs an action indicating that the program should stop (for example, by clicking glBegin(GL_TRIANGLES); a button to quit the application). This stage may involve tasks such as glVertex3f(10.0, 90.0, 0.0); signaling the application to stop checking for user input and closing glVertex3f(10.0, 10.0, 0.0); any windows created by the application. glVertex3f(35.0, 75.0, 0.0); glVertex3f(30.0, 20.0, 0.0); Pygame is a set of Python modules designed for creating video games. It is a glVertex3f(90.0, 90.0, 0.0); popular Python game development library. glVertex3f(80.0, 40.0, 0.0); glEnd(); To set up a window using Pygame, use the pygame.display.set_mode() method. It requires two (2) parameters to define the width and height of the Each of the triangle’s vertices is specified by a call to the function glVertex3f. window. Below is an example: Vertices must be specified between calls to glBegin and glEnd. The screen = pygame.display.set_mode((500, 500)) parameter to glBegin tells which type of primitive is being drawn. A point is a location in space. It is the most basic graphical element. To render Uniform Data a single point on the screen, use a vertex shader. A vertex shader will consist In computer graphics, there are many scenarios where you may want to of the following code using the OpenGL Shading Language (GLSL). repeatedly use the same information. For example, you may want to translate void main() all the vertices that define a shape by the same amount. You may also want { to draw all the pixels corresponding to a shape with the same color. The most gl_Position = vec4(0.0, 0.0, 0.0, 1.0); flexible and efficient way to accomplish such tasks is by using uniform } variables. Uniform variables are global variables that can be accessed by the vertex shader or the fragment shader, and whose values are constant while each shape is being drawn (can be changed between draw function calls). 02 Handout 1 *Property of STI  [email protected] Page 1 of 2  IT2202 Uniform shader variables, declared with the type qualifier uniform, provide a mechanism for directly sending data from variables in a CPU application to variables in a GPU program. You must obtain a reference to the location of the uniform variable before data may be sent to it. This is accomplished with the following OpenGL function: glGetUniformLocation(programRef, variableName) The glGetUniformLocation function returns a value used to reference a uniform variable (indicated by the type qualifier uniform) with the name indicated by the parameter variableName and declared in the program referenced by the parameter programRef. If the variable is not declared or not used in the specified program, -1 is returned. Interactivity The Pygame library provides support for working with user input events. Pygame detects keydown events and keyup events. Keydown events occur the moment a key is initially pressed, while keyup events occur the moment the key is released. An event is said to be discrete if it happens once at an isolated point in time. It is said to be continuous if it continues happening during an interval of time. The keydown and keyup events are discrete, but many applications also feature continuous actions (such as moving an object on the screen) that occur for as long as a key is being held down. The following is a sample code that checks if a keydown event occurs. if event.type == pygame.KEYDOWN: if event.key == pygame.K_w: print("Player moved up!") elif event.key == pygame.K_a: print("Player moved left!") elif event.key == pygame.K_s: print("Player moved down!") elif event.key == pygame.K_d: print("Player moved right!") References: Korites, B. (2018). Python graphics: A reference for creating 2D and 3D images. Apress. Marschner, S. & Shirley, P. (2021). Fundamentals of computer graphics (5th ed.). CRC Press. Stemkoski, L. & Pascale, M. (2021). Developing graphics frameworks with Python and OpenGL. CRC Press. 02 Handout 1 *Property of STI  [email protected] Page 2 of 2