OpenGL ES 101

© Copyright Khronos Group, 2004 - Page 1

OpenGL ES 101OpenGL ES 101

Dave Astle, GameDev.net, [email protected], [email protected]


OutlineOutline• Background• OpenGL ES 1.0 vs. OpenGL• OpenGL ES 1.0 Extensions• What’s new in OpenGL 1.1• Learning more


Why OpenGL ES?Why OpenGL ES?• Need for a standard 3D graphics API for a wide range of devices

- Low processing power- Limited memory- Battery powered (usually)- Low resolution

• OpenGL is a natural fit- However, needed modifications to be suitable for low-power, relatively limited devices

• Based on OpenGL 1.3- Removed redundant APIs- Removed features that were too expensive or unused- Removed some data types- Added smaller data types for some APIs- Added support for fixed point

• Common vs. Common-lite profiles- Common-lite doesn’t support floating point




Vertex SpecificationVertex SpecificationIn• glColor4f

• glNormal3f

• glMultiTexCoord4f

Out• Immediate Mode

- glBegin/glEnd, glVertex, glTexCoord

• Color index mode


Vertex ArraysVertex ArraysIn• glVertexPointer• glNormalPointer• glTexCoordPointer• glColorPointer• glDrawArrays• glDrawElements• glClientActiveTexture• glEnableClientState• glDisableClientState

Out• glEdgeFlagPointer• glIndexPointer• glArrayElement• glInterleavedArrays• glDrawRangeElements• Quads, quad strips, and polygons


TransformationTransformationIn• glDepthRange• glViewport• glMatrixMode (except color)• glLoadMatrixf• glRotatef• glScalef• glTranslatef• glFrustum• glOrtho• glActiveTexture• glPush/PopMatrix• GL_RESCALE_NORMAL,

GL_NORMALIZE

Out• glLoadTransposeMatrix• glMultTransposeMatrix• glTexGen• glGetTexGen


Materials and LightingMaterials and LightingIn• glFrontFace• GL_LIGHTING, GL_LIGHT{0-7}• glMaterialf[v]

- GL_FRONT_AND_BACK only

• glLightf[v]• glLightModelf[v]

- GL_LIGHT_MODEL_TWO_SIDE- GL_AMBIENT

• GL_COLOR_MATERIAL• glShadeModel

Out• glGetMaterial• glGetLight• glLightModel

- GL_LIGHT_MODEL_COLOR_CONTROL- GL_LIGHT_MODEL_LOCAL_VIEWER

• glColorMaterial


Points, Lines, and PolygonsPoints, Lines, and PolygonsIn• glPointSize• GL_POINT_SMOOTH• glLineWidth• GL_LINE_SMOOTH• Culling• glPolygonOffset

Out• Line and polygon stippling• Polygon antialiasing• glPolygonMode

- No point or line mode


Pixels and BitmapsPixels and BitmapsIn• glPixelStorei

- For loading textures and reading from the screen

- Only supports GL_PACK_ALIGNMENT and GL_UNPACK_ALIGNMENT

• glReadPixels- Limited number of formats

Out• Imaging subset (filters, histograms,

minmax)• glDrawPixels• glCopyPixels• glPixelZoom• glBitmap• glRasterPos


TexturesTexturesIn• Most common formats

- GL_RGB, GL_RGBA, GL_LUMINANCE, GL_ALPHA, GL_LUMINANCE_ALPHA

- 16-bit formats (packed pixel), 24 bits, 32 bits

• 2D textures- glTexImage2D- glTexSubImage2D- glCopyTexImage2D- glCopyTexSubImage2D

• Compressed 2D textures- glCompressedTexImage2D- glCOmpressedTexSubImage2D- Spec doesn’t define any compression standard- Does include paletted textures as req. extension

• Texture parameters- All filtering modes (including mipmaps)- Clamp-to-edge and repeat wrap modes

• Texture environment modes- Modulate, replace, add, decal, blend

Out• 1D & 3D textures• Cube maps• Texture parameters

- No LOD control- No texture border- Thus, no clamp-to-border or clamp wrap modes

• Texture priorities- glPrioritizeTextures- glAreTexturesResident

• Dynamic texture state queries- glGetTexImage- glGetCompressedTexImage- glGetTexParameter- glGetTexLevelParameter- glGetTexEnv- glIsTexture


Per-fragment OperationsPer-fragment OperationsIn• Scissor test

- glEnable(GL_SCISSOR_TEST), glScissor• Multisampling

- glEnable(GL_MULTISAMPLE), glSampleCoverage

• Alpha test- glEnable(GL_ALPHA_TEST), glAlphaFunc

• Stencil test- Implementations aren’t required to have a

stencil buffer• Depth test

- Implementations aren’t required to have a depth buffer

• Blending- Mostly

• Dithering- Implementation may ignore it

• Logic ops (non-indexed only)- glColorLogicOp

Out• Some control over blending

- glBlendEquation- glBlendColor


Framebuffer OperationsFramebuffer OperationsIn• Color masking

- glColorMask

• Clears- glClear- glClearColor- glClearDepth- glClearStencil

Out• glDrawBuffer• glReadBuffer• Accumulation buffer

- glAccum


More inMore in• glFlush• glFinish• glHint• glGetString• glGetIntegerv

- Limited to static states

• Fog- glFog- Indexed fog not supported- Will probably be done per-vertex rather than per-pixel


More outMore out• Evaluators• Selection• Feedback• Display lists• Rectangles

- glRect

• Clip planes• Most state queries

- glGetBooleanv/glGetDoublev/glGetFloatv- glIsEnabled

• Attribute stacks- glPush/PopAttrib- glPush/PopClientAttrib




OpenGL ES 1.0 ExtensionsOpenGL ES 1.0 Extensions• Divided into core additions, required, and optional• OES_byte_coordinates (core)

- Allows the use of bytes in vertex and texcoord arrays

• OES_fixed_point (core)- For every function taking a float, there’s now a function accepting fixed

- e.g. glClearColorx, glTexParameterx- New type: GL_FIXED (s15.16)

• OES_single_precision (core)- No doubles in OpenGL ES so…- Added several new functions to replace functions that only accept doubles

- e.g. glFrustum

• OES_read_format (required)- Allows implementation to specify preferred forma/typet for glReadPixels- This is in addition to the required format/type of GL_RGBA/GL_UNSIGNED_BYTE- Queried by passing GL_IMPLEMENTATION_READ_FORMAT_OES and

GL_IMPLEMENTATION_READ_TYPE_OES to glGetIntegerv()


OpenGL ES 1.0 Extensions (cont)OpenGL ES 1.0 Extensions (cont)• OES_compressed_paletted_texture

- Allows the use of textures composed of palettes of 16 or 256 entries in 5 different formats (24-bit RGB, 32-bit RGBA, RGB565, RGB5551, RGB4444)

- Specified using the glCompressedTexImage2D API

• OES_query_matrix (optional)- Allows an app to read the current value of any matrix stack- API allows the implementation to report representation as accurately as possible without using

floats:GLbitfield glQueryMatrixxOES(GLfixed mantissa[16], GLint exponent[16])

- Matrix component i = mantissa[i] * 2 ^ exponent[i]- Invalid matrix elements are identified in return value




OpenGL ES 1.1OpenGL ES 1.1• Released at SIGGRAPH last month

• Based on OpenGL 1.5 specification

• Many changes added with hardware support in mind

• Adds features to OpenGL ES 1.0- Higher quality rendering options- Performance optimizations- Reduces memory bandwidth and power consumption


What’s new in OpenGL ES 1.1?What’s new in OpenGL ES 1.1?• Vertex buffer objects

- Subset of OpenGL 1.5 VBOs – no read or copy, no stream draw, no memory mapping

• User clip planes- At least one

• Point parameters• Greatly improved multitexture support

- At least two texture units supported- All GL_COMBINE modes supported except for crossbar

• Automatic mipmap generation• Blend squaring• glColor4ub and glColor4ubv• Almost all dynamic and static state queries are now supported


What wasn’t included?What wasn’t included?• Occlusion queries• Secondary color• Fog coordinates• Multi draw arrays/elements• Mirrored repeat wrap mode• LOD bias• Depth textures and shadow mapping operations• No shaders (yet)


OpenGL ES 1.1 ExtensionsOpenGL ES 1.1 Extensions• OES_matrix_get (core)

- Replaces OES_query_matrix- Allows Common-lite profiles to report floating point representation without requiring floating point

support in the profile- Values are returned encoded in ints, using IEEE 734 representation

- Adds GL_MODELVIEW_MATRIX_FLOAT_AS_INT_BITS_OES, GL_PROJECTION_MATRIX_FLOAT_AS_INT_BITS_OES, and GL_TEXTURE_MATRIX_FLOAT_AS_INT_BITS_OES tokens to be passed to glGetIntegerv

• OES_point_sprite (required)- Very similar to ARB_point_sprite and NV_point_sprite extensions- Used with point size and point size attenuation

• OES_point_size_array (required)- Adds additional vertex attribute/array for point sizes- Used with point sprites to specify sprites of different sizes


OpenGL ES 1.1 Extensions (cont.)OpenGL ES 1.1 Extensions (cont.)• OES_matrix_palette (optional)

- Simplified ARB_matrix_palette

- Palette contains up to GL_MAX_PALETTE_MATRICES_OES matrices

- Matrices added to palette by setting the matrix mode to GL_MATRIX_PALETTE_OES and using glCurrentPaletteMatrixOES and existing matrix functions

- Can also load from the current modelview matrix with glLoadPaletteFromModelViewMatrixOES

- Each vertex can have up to GL_MAX_VERTEX_UNITS_OES matrix indices and weights

- Per-vertex indices and weights specified with:- glMatrixIndexPointerOES- glWeightPointerOES


OpenGL ES 1.1 Extensions (cont.)OpenGL ES 1.1 Extensions (cont.)• OES_draw_texture (optional)

- Allows fast rendering of 2D elements by taking advantage of existing texture hardware

- Adds a texture crop rectangle per texture object- Set by using GL_TEXTURE_CROP_RECT_OES with glTexParameteriv

- The region in the crop triangle is drawn using glDrawTexOES- Interface allows the image to be stretched or shrunk- Z value can be controlled, but is constant across the surface- Causes fragments to be generated for the specified window region

- No different from normal fragments- All active texture units are applied, using filtering modes and texture environment- Current color applied- Eye depth is 0 for fog computation, though this can be changed if EXT_fog_coord is supported




Learning moreLearning more• OpenGL ES website: www.opengles.org or www.khronos.org

• OpenGL ES Game Development, Course Technology PTR, Sept. ‘04


Questions?Questions?

OpenGL ES 101

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