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Text File | 1996-11-11 | 17.6 KB | 437 lines

Name EXT_texture Name Strings GL_EXT_texture Version $Date: 1995/09/30 02:32:31 $ $Revision: 1.1 $ Number 4 Dependencies None Overview The original intention of this extension was simply to support various numeric resolutions of color components in texture images. While it accomplishes this, it also accomplishes a larger task, that of formalizing the notion of an internal format for images, corresponding to the external format that already existed for image data in host memory. This notion of an internal image format will be used extensively in later extensions, especially those concerned with pixel manipulation. The idea of an internal format is simple: rather than treating a retained image as having 1, 2, 3, or 4 components, treat it as though it has a specific format, such as LUMINANCE_ALPHA, or just ALPHA. Then define the semantics of the use of internal images with these formats in a consistent way. Because texture mapping is already defined in GL, the semantics for internal-format images were chosen to match those of the 1, 2, 3, and 4 component internal images that already existed. The new semantics are a superset of the old ones, however, so this extension adds capabilities to GL, as well as allowing internal resolutions to be specified. This extension also defines a robust method for applications to determine what combinations of texture dimensions and resolutions are supported by an implementation. It also introduces a new texture environment: REPLACE_EXT. New Procedures and Functions None New Tokens Accepted by the <components> parameter of TexImage1D and TexImage2D: ALPHA4_EXT 0x803B ALPHA8_EXT 0x803C ALPHA12_EXT 0x803D ALPHA16_EXT 0x803E LUMINANCE4_EXT 0x803F LUMINANCE8_EXT 0x8040 LUMINANCE12_EXT 0x8041 LUMINANCE16_EXT 0x8042 LUMINANCE4_ALPHA4_EXT 0x8043 LUMINANCE6_ALPHA2_EXT 0x8044 LUMINANCE8_ALPHA8_EXT 0x8045 LUMINANCE12_ALPHA4_EXT 0x8046 LUMINANCE12_ALPHA12_EXT 0x8047 LUMINANCE16_ALPHA16_EXT 0x8048 INTENSITY_EXT 0x8049 INTENSITY4_EXT 0x804A INTENSITY8_EXT 0x804B INTENSITY12_EXT 0x804C INTENSITY16_EXT 0x804D RGB2_EXT 0x804E RGB4_EXT 0x804F RGB5_EXT 0x8050 RGB8_EXT 0x8051 RGB10_EXT 0x8052 RGB12_EXT 0x8053 RGB16_EXT 0x8054 RGBA2_EXT 0x8055 RGBA4_EXT 0x8056 RGB5_A1_EXT 0x8057 RGBA8_EXT 0x8058 RGB10_A2_EXT 0x8059 RGBA12_EXT 0x805A RGBA16_EXT 0x805B Accepted by the <pname> parameters of GetTexLevelParameteriv and GetTexLevelParameterfv: TEXTURE_RED_SIZE_EXT 0x805C TEXTURE_GREEN_SIZE_EXT 0x805D TEXTURE_BLUE_SIZE_EXT 0x805E TEXTURE_ALPHA_SIZE_EXT 0x805F TEXTURE_LUMINANCE_SIZE_EXT 0x8060 TEXTURE_INTENSITY_SIZE_EXT 0x8061 Accepted by the <params> parameter of TexEnvf, TexEnvi, TexEnvfv, and TexEnvfi when the <pname> parameter value is GL_TEXTURE_ENV_MODE REPLACE_EXT 0x8062 Accepted by the <target> parameters of TexImage1D, GetTexLevelParameteriv, and GetTexLevelParameterfv: PROXY_TEXTURE_1D_EXT 0x8063 Accepted by the <target> parameters of TexImage2D, GetTexLevelParameteriv, and GetTexLevelParameterfv: PROXY_TEXTURE_2D_EXT 0x8064 Additions to Chapter 2 of the GL Specification (OpenGL Operation) A new error token value, TEXTURE_TOO_LARGE_EXT, is defined and added to table 2.3: Offending command Error Description ignored? ----- ----------- --------- INVALID_ENUM enum argument out of range Yes INVALID_VALUE Numeric argument out of range Yes INVALID_OPERATION Operation illegal in current state Yes STACK_OVERFLOW Command would cause a stack overflow Yes STACK_UNDERFLOW Command would cause a stack underflow Yes TEXTURE_TOO_LARGE_EXT The specified texture is too large Yes OUT_OF_MEMORY Not enough memory left to execute command Unknown Table 2.3: Summary of GL errors and defined as follows: TEXTURE_TOO_LARGE_EXT 0x8065 Additions to Chapter 3 of the GL Specification (Rasterization) Many additional values can be specified for the <components> parameter of TexImage1D and TexImage2D. The GL Specification indicates (in section 3.8) that only values 1, 2, 3, and 4 can be specified. This extension defines semantics for the currently existing tokens ALPHA, RGB, RGBA, LUMINANCE, and LUMINANCE_ALPHA, and also defines semantics for many new tokens. Each of the new tokens (except INTENSITY_EXT) indicates a desired storage resolution, as well as a base format. These tokens are: Red Green Blue Alpha Luminance Intensity Token name Base format Bits Bits Bits Bits Bits Bits ---------- ----------- ---- ---- ---- ---- ---- ---- ALPHA4_EXT ALPHA 4 ALPHA8_EXT ALPHA 8 ALPHA12_EXT ALPHA 12 ALPHA16_EXT ALPHA 16 LUMINANCE4_EXT LUMINANCE 4 LUMINANCE8_EXT LUMINANCE 8 LUMINANCE12_EXT LUMINANCE 12 LUMINANCE16_EXT LUMINANCE 16 LUMINANCE4_ALPHA4_EXT LUMINANCE_ALPHA 4 4 LUMINANCE6_ALPHA2_EXT LUMINANCE_ALPHA 6 2 LUMINANCE8_ALPHA8_EXT LUMINANCE_ALPHA 8 8 LUMINANCE12_ALPHA4_EXT LUMINANCE_ALPHA 4 12 LUMINANCE12_ALPHA12_EXT LUMINANCE_ALPHA 12 12 LUMINANCE16_ALPHA16_EXT LUMINANCE_ALPHA 16 16 INTENSITY_EXT INTENSITY ? INTENSITY4_EXT INTENSITY 4 INTENSITY8_EXT INTENSITY 8 INTENSITY12_EXT INTENSITY 12 INTENSITY16_EXT INTENSITY 16 RGB2_EXT RGB 2 2 2 RGB4_EXT RGB 4 4 4 RGB5_EXT RGB 5 5 5 RGB8_EXT RGB 8 8 8 RGB10_EXT RGB 10 10 10 RGB12_EXT RGB 12 12 12 RGB16_EXT RGB 16 16 16 RGBA2_EXT RGBA 2 2 2 2 RGBA4_EXT RGBA 4 4 4 4 RGB5_A1_EXT RGBA 5 5 5 1 RGBA8_EXT RGBA 8 8 8 8 RGB10_A2_EXT RGBA 10 10 10 2 RGBA12_EXT RGBA 12 12 12 12 RGBA16_EXT RGBA 16 16 16 16 All implementations of this extension support the base formats ALPHA, LUMINANCE, LUMINANCE_ALPHA, RGB, and RGBA. All implementations also accept all the tokens in the table above, but may not allocate storage exactly equal to that indicated in the table. Instead, storage is allocated to best match the resolutions in the table. The determination of best match is left to the implementation. Storage allocation for the base formats (as well as for formats "1", "2", "3", and "4") is an implementation dependent compromise of component resolution, performance, image size, and memory availability. It is acceptable for an implementation to vary its allocation of internal component resolution based on any TexImage1D or TexImage2D parameter, but the allocation must not be a function of any other factor, and cannot be changed once it is established. In particular, allocations must be invariant -- the same allocation must be made each time a texture image is specified with the same parameter values. Provision is made for an application to determine what component resolutions are available without having to fully specify the texture (see below). A set of mipmap arrays is incomplete (see the Mipmapping section of the GL Specification) if different internal formats are specified for arrays in the set, even if the resulting formats of the arrays are identical. An implementation can, however, report different component precisions for the arrays in the set, even if all were specified with the same internal format. (The set of arrays will be complete in this case.) The assignments of texture component values from color components "extracted" from the incoming image (see the discussion in section 3.8 of the GL Specification) are defined by this new version of Table 3.6: Base Internal Format red green blue alpha luminance intensity -------------------- --- ----- ---- ----- --------- --------- ALPHA A LUMINANCE R LUMINANCE_ALPHA A R INTENSITY R RGB R G B RGBA R G B A Table 3.6: Correspondence of texture components to extracted R, G, B, and A values. Texture components are assigned to Rt, Gt, Bt, and At. Table 3.8 (Texture functions) refers to these components. The assignments are defined by the following table: Texture Environment ------------------- Base Texture Format Rt Gt Bt At ------------------- -- -- -- -- LUMINANCE Lt Lt Lt x ALPHA x x x At INTENSITY It It It It LUMINANCE_ALPHA Lt Lt Lt At RGB Rt Gt Bt x RGBA Rt Gt Bt At Table ??: Mapping of Texture Components to Rt, Gt, Bt, At. Where there appears an "x", the assignment is "don't care", since that component is not used by the texture environment. This extension redefines the application of a texture to the color components of a fragment. In particular, a new texture environment, REPLACE, and two new texture formats, ALPHA and INTENSITY, are included. Table 3.8 (Texture functions) of the GL Specification is replaced by the following table: Texture Environment ------------------- Base Texture Format REPLACE MODULATE BLEND DECAL ------------------- ------- -------- ----- ----- LUMINANCE Rv = Rt Rv = Rf * Rt Rv = Rf * (1-Rt) + Rc * Rt undefined Gv = Gt Gv = Gf * Gt Gv = Gf * (1-Gt) + Gc * Gt Bv = Bt Bv = Bf * Bt Bv = Bf * (1-Bt) + Bc * Bt Av = Af Av = Af Av = Af ALPHA Rv = Rf Rv = Rf Rv = Rf undefined Gv = Gf Gv = Gf Gv = Gf Bv = Bf Bv = Bf Bv = Bf Av = At Av = Af * At Av = Af * At INTENSITY Rv = Rt Rv = Rf * Rt Rv = Rf * (1-Rt) + Rc * Rt undefined Gv = Gt Gv = Gf * Gt Gv = Gf * (1-Gt) + Gc * Gt Bv = Bt Bv = Bf * Bt Bv = Bf * (1-Bt) + Bc * Bt Av = At Av = Af * At Av = Af * (1-At) + Ac * At LUMINANCE_ALPHA Rv = Rt Rv = Rf * Rt Rv = Rf * (1-Rt) + Rc * Rt undefined Gv = Gt Gv = Gf * Gt Gv = Gf * (1-Gt) + Gc * Gt Bv = Bt Bv = Bf * Bt Bv = Bf * (1-Bt) + Bc * Bt Av = At Av = Af * At Av = Af * At RGB Rv = Rt Rv = Rf * Rt Rv = Rf * (1-Rt) + Rc * Rt Rv = Rt Gv = Gt Gv = Gf * Gt Gv = Gf * (1-Gt) + Gc * Gt Gv = Gt Bv = Bt Bv = Bf * Bt Bv = Bf * (1-Bt) + Bc * Bt Bv = Bt Av = Af Av = Af Av = Af Av = Af RGBA Rv = Rt Rv = Rf * Rt Rv = Rf * (1-Rt) + Rc * Rt Rv = Rf * (1-At) + Rt * At Gv = Gt Gv = Gf * Gt Gv = Gf * (1-Gt) + Gc * Gt Gv = Gf * (1-At) + Gt * At Bv = Bt Bv = Bf * Bt Bv = Bf * (1-Bt) + Bc * Bt Bv = Bf * (1-At) + Bt * At Av = At Av = Af * At Av = Af * At Av = Af Table 3.8: Texture functions. Finally, for backward compatibility, the semantics of <components> values 1, 2, 3, and 4 are identical to those of LUMINANCE, LUMINANCE_ALPHA, RGB, and RGBA respectively. The one exception is that the token values for 1, 2, 3, and 4 are not the same as the token values LUMINANCE, LUMINANCE_ALPHA, RGB, and RGBA. Query support ------------- Alternate sets of per-level texture state are defined for the proxy textures PROXY_TEXTURE_1D_EXT and PROXY_TEXTURE_2D_EXT. When TexImage2D is called with <target> set to PROXY_TEXTURE_2D_EXT, proxy state values TEXTURE_WIDTH, TEXTURE_HEIGHT, TEXTURE_BORDER, TEXTURE_COMPONENTS, TEXTURE_RED_SIZE_EXT, TEXTURE_GREEN_SIZE_EXT, TEXTURE_BLUE_SIZE_EXT, TEXTURE_ALPHA_SIZE_EXT, TEXTURE_LUMINANCE_SIZE_EXT, and TEXTURE_INTENSITY_SIZE_EXT are always recomputed and updated, even if the texture is too large to actually be used. If the texture is too large, all of these state variables are set to zero. If the texture could be accommodated by TexImage2D called with <target> TEXTURE_2D, these values are set as though TEXTURE_2D were being defined. All of these state value can be queried with GetTexLevelParameteriv or GetTexLevelParameterfv with <target> set to PROXY_TEXTURE_2D_EXT. Calling TexImage2D with <target> PROXY_TEXTURE_2D_EXT has no effect on the actual 2-dimensional texture or its state. To determine the maximum array size for a mipmap texture, specify and query the proxy texture at the highest level that accurately reflects the aspect ratio of the desired level zero array. There is no image associated with PROXY_TEXTURE_2D_EXT. Therefore PROXY_TEXTURE_2D_EXT cannot be used as a texture, and its image must never be queried using GetTexImage. (The error INVALID_ENUM results if this is attempted.) Likewise, there is no nonlevel-related state associated with a proxy texture, so calling GetTexParameteriv or GetTexParameterfv with <target> PROXY_TEXTURE_2D_EXT results in the error INVALID_ENUM. The proxy 1-dimensional texture behaves identically to the proxy 2-dimensional texture, except that its state does not include TEXTURE_HEIGHT. Additions to Chapter 4 of the GL Specification (Per-Fragment Operations and the Framebuffer) None Additions to Chapter 5 of the GL Specification (Special Functions) None Additions to Chapter 6 of the GL Specification (State and State Requests) GetTexLevelParameteriv, when called with <pname> TEXTURE_COMPONENTS, returns the value of the <components> state variable as specified by the application. This remains true even if the actual internal format matches that of another token. GetTexLevelParameteriv, when called with <pname> TEXTURE_RED_SIZE_EXT, TEXTURE_GREEN_SIZE_EXT, TEXTURE_BLUE_SIZE_EXT, TEXTURE_ALPHA_SIZE_EXT, TEXTURE_LUMINANCE_SIZE_EXT, or TEXTURE_INTENSITY_SIZE_EXT returns the actual number of bits of internal storage for red, green, blue, alpha, luminance, or intensity. This value may not match the value of the specified internal format. GetTexImage continues to operate as though ReadPixels were called with the texture image as the framebuffer. The assignments of texture component values to the initial R, G, B, and A values of the read-back texel (prior to PixelTransfer and PixelStorage operations) are: Base Internal Format R G B A -------------------- - - - - ALPHA 0.0 0.0 0.0 alpha LUMINANCE luminance 0.0 0.0 0.0 LUMINANCE_ALPHA luminance 0.0 0.0 alpha INTENSITY intensity 0.0 0.0 0.0 RGB red green blue 0.0 RGBA red green blue alpha Additions to the GLX Specification None GLX Protocol None Dependencies on EXT_abgr Token ABGR_EXT cannot be used to specify internal texture image formats. Errors The GL Specification requires that INVALID_VALUE be generated if any texture dimension is specified less than zero, greater than MAX_TEXTURE_SIZE, or with a value that cannot be represented as 2**k + 2*border, for some integer k. This extension eliminates the requirement that all dimensions be specified less than or equal to MAX_TEXTURE_SIZE, and replaces it with a new error token and error condition. INVALID_VALUE is generated if any texture dimension is specified less than zero, or with a value that cannot be represented as 2**k + 2*border. TEXTURE_TOO_LARGE_EXT is generated if the texture is too large to be accommodated, for whatever reason. An implementation must specify MAX_TEXTURE_SIZE such that TEXTURE_TOO_LARGE_EXT is never generated if all the dimensions of the texture are less than or equal to MAX_TEXTURE_SIZE. Also, TEXTURE_TOO_LARGE_EXT is never generated when the target is a proxy texture, such as PROXY_TEXTURE_1D_EXT or PROXY_TEXTURE_2D_EXT. This change to the error semantics does not require that the major revision level be incremented, because the GL Specification allows for changes to error semantics (Section 2.5). New State Initial Get Value Get Command Type Value Attrib --------- ----------- ---- ------- ------ TEXTURE_RED_SIZE_EXT GetTexLevelParameteriv 2 x 2 x levels x Z+ 0 - TEXTURE_GREEN_SIZE_EXT GetTexLevelParameteriv 2 x 2 x levels x Z+ 0 - TEXTURE_BLUE_SIZE_EXT GetTexLevelParameteriv 2 x 2 x levels x Z+ 0 - TEXTURE_ALPHA_SIZE_EXT GetTexLevelParameteriv 2 x 2 x levels x Z+ 0 - TEXTURE_LUMINANCE_SIZE_EXT GetTexLevelParameteriv 2 x 2 x levels x Z+ 0 - TEXTURE_INTENSITY_SIZE_EXT GetTexLevelParameteriv 2 x 2 x levels x Z+ 0 - TEXTURE GetTexImage 2 x 1 x levels x I null - TEXTURE_WIDTH GetTexLevelParameteriv 2 x 2 x levels x Z+ 0 - TEXTURE_HEIGHT GetTexLevelParameteriv 1 x 2 x levels x Z+ 0 - TEXTURE_BORDER GetTexLevelParameteriv 2 x 2 x levels x Z+ 0 - TEXTURE_COMPONENTS GetTexLevelParameteriv 2 x 2 x levels x Z42 1 - New Implementation Dependent State None