OpenGL

Opengl

OpenGL has been around for over 16 years. Its development is overseen by the Khronos group.

OpenGL has undergone some radical changes in its most recent release.

OpenGL Architecture

internal state machine

In programmable it is up to the programmer to not only pass in the correct information (for example the color of the vertex) but also apply this information to the vertex in the shader.

What is opengl?

Pipeline

Fixed-Function vs. Programmability

Related Libraries

GLUT (OpenGL Utility Toolkit)

SDL

GLUT

OpenGL Utility Toolkit

windowing, menus, or input

SDL

The Simple Direct Media Layer

audio, input, 2D graphics, and many other things

WGL

prevent multiple OpenGL applications from interfering with each other. This is done through the use of a rendering context

Only one rendering context per thread.

HGLRC wglCreateContext(HDC hDC);

BOOL wglDeleteContext(HGLRC hRC);

BOOL wglMakeCurrent(HDC hDC, HGLRC hRC);

WGL

HGLRC wglGetCurrentContext();

HDC wglGetCurrentDC();

Pixel Formats

typedef struct tagPIXELFORMATDESCRIPTOR {

WORD nSize;WORD nVersion;DWORD dwFlags;BYTE iPixelType;BYTE cColorBits;BYTE cRedBits;BYTE cRedShift;BYTE cGreenBits;BYTE cGreenShift; BYTE cBlueBits;BYTE cBlueShift;BYTE cAlphaBits;BYTE cAlphaShift; BYTE cAccumBits;BYTE cAccumRedBits; BYTE cAccumGreenBits; BYTE cAccumBlueBits; BYTE cAccumAlphaBits; BYTE cDepthBits;BYTE cStencilBits; BYTE cAuxBuffers; BYTE iLayerType;BYTE bReserved;DWORD dwLayerMask; DWORD dwVisibleMask; DWORD dwDamageMask;

} PIXELFORMATDESCRIPTOR;

Pixel Formats

nSize

dwFlags

iPixelType PFD_TYPE_RGBA. RGBA pixels. Each pixel has four components in this order: red, green, blue, and alpha.

PFD_TYPE_COLORINDEX. Paletted mode. Each pixel uses a color-index value.

• cColorBits the bits per pixel

Setting the Pixel Format

int ChoosePixelFormat(HDC hdc, CONST PIXELFORMATDESCRIPTOR *ppfd); (modify pixel format to match supported and return id for pixel format)

BOOL SetPixelFormat(HDC hdc, int pixelFormat, const PIXELFORMATDESCRIPTOR *ppfd);

State Functions

void glGetBooleanv(GLenum pname, GLboolean *params); void glGetDoublev(GLenum pname, GLdouble *params); void glGetFloatv(GLenum pname, GLfloat *params); void glGetIntegerv(GLenum pname, GLint *params);

Enabling and Disabling States

void glEnable(GLenum cap);

void glDisable(GLenum cap);

GLboolean glIsEnabled(GLenum cap);

Querying String Values

const GLubyte *glGetString(GLenum name);

GL_VENDOR , GL_RENDERER , GL_VERSION , GL_EXTENSIONS

Finding Errors

GLenum glGetError();

Colors in OpenGL

void glColor (T components);

void glColorv(T components);

Primitives

Handling Primitives

Immediate Mode

Vertex Arrays

Immediate Mode

void glBegin(GLenum mode);

glBegin()

glEnd()

GL_INVALID_OPERATION

void glVertex{234}{dfis}();

void glVertex{234}{dfis}v();

Demo 1

Vertex Arrays

void glEnableClientState(GLenum cap);

void glDisableClientState(GLenum cap);

gl*Pointer()

void glVertexPointer(GLint size, GLenum type, GLsizei stride, const GLvoid *array);

size must be 2, 3, or 4 and

Type can be set to GL_SHORT, GL_INT, GL_FLOAT, or GL_DOUBLE.

Stride padding in bytes between each vertex

Vertex Arrays

void glColorPointer(GLint size, GLenum type, GLsizei stride, const GLvoid *array);

void glEdgeFlagPointer(GLsizei stride, const GLboolean *array);

Array of Boolean

void glNormalPointer(GLenum type, GLsizei stride, const GLvoid *array); normals always (x,y,z) so no need for the size.

void glTexCoordPointer(GLint size, GLenum type, GLsizei stride, const GLvoid *array); size = number of coordinate per vertex

Rendering Uesing Vertex Arrays

void glDrawArrays(GLenum mode, GLint first, GLsizei count);

void glDrawElements(GLenum mode, GLsizei count, GLenum type, const GLvoid *indices); [count is the number of indices that you want to render ]

void glDrawRangeElements(GLenum mode, GLuint start, GLuint end, GLsizei count, GLenum type, const GLvoid * indices);

Demo vertix_with_indcies

Rendering Uesing Vertex Arrays

void glMultiDrawArrays(GLenum mode, GLint *first, GLsizei *count, GLsizei primcount)

Vertex Buffer Objects

(VRAM) instead of (RAM)

To use a VBO, you need to perform the following steps:

1. Generate a name for the buffer.

2. Bind (activate) the buffer.

3. Store data in the buffer.

4. Use the buffer to render the data. 5. Destroy the buffer.

5. Destroy the buffer.

Generating a Name

void glGenBuffers(GLsizei n, GLuint *buffers);

void glDeleteBuffers(GLsizei n, const GLuint *buffers);

Binding the Buffer

Binding a buffer makes it current; all buffer-related OpenGL calls and rendering will operate on the currently bound buffer.

void glBindBuffer(GLenum target, GLuint buffer);

target can be GL_ARRAY_BUFFER, GL_ELEMENT_ARRAY_BUFFER, GL_PIXEL_PACK_BUFFER, or GL_PIXEL_UNPACK_BUFFER

GL_ARRAY_BUFFER for vertices data and GL_ELEMENT_ARRAY_BUFFER for indices data.

if buffer is zero, the call will unbind any currently bound buffer.

Filling the Buffer

void glBufferData(GLenum target, GLsizeiptr size, const GLvoid *data, GLenum usage);

usage is a hint to OpenGL telling it how you intend to use this buffer. It can be GL_STREAM_DRAW, GL_STREAM_READ, GL_STREAM_COPY, GL_STATIC_DRAW, GL_STATIC_READ, GL_STATIC_COPY, GL_DYNAMIC_DRAW, GL_DYNAMIC_READ, or GL_DYNAMIC_COPY

Calling glBufferData() on a buffer object that already contains data will cause the old data to be destroyed and replaced with the new data

Rendering with Buffers and Vertex Arrays

When rendering with VBOs you use gl*Pointer() functions as an offset.

Demo simple point

Modifying Point Size

void glPointSize(GLfloat size)

If point anti-aliasing is disabled then the point size is rounded to the nearest integer never zero.