Samsung S5PC100, Руководство пользователя

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3D-ACCELERATOR S5PC100 USER’S MANUAL (REV1.0)
9.6-26
3.3 HOW TO TRANSFER GEOMETRY DATA
A geometry data is transferred from CPU or from the Vertex Buffer in the Host Interface after special registers for
Host Interface are set (explained in the next section). The geometry data is a set of input attributes to vertex
shader. In other words, a number of attributes for a vertex can be transferred from CPU or from the Vertex Buffer.
(From time to time, a vertex can have only an attribute.) A set of attributes constituting of a vertex is defined in
HI_ATTRIB0~HI_ATTRIB9. The number of components in each attributes is determined by
HI_ATTRIB
n .NumComp. The LastAttr bit in HI_ATTRIB n represents whether the HI_ATTRIB n is used or not. For
example, HI_ATTRIB0.LastAttr = HI_ATTRIB1.LastAttr = HI_ATTRIB2.LastAttr = 0 and HI_ATTRIB3.LastAttr = 1
mean that a vertex is composed of 4 attributes. (HI_ATTRIB4.LastAttr and so on do not determine the number of
attributes for a vertex.)
The number of vertices (count) is transferred only by CPU. (The count is written into HI_DWENTRY of the Host
Interface.) Then, CPU can transfer indices or raw geometry data into the same HI_DWENTRY. However, the
Vertex Buffer can feed only geometry data to the Host Interface. The usage of the Vertex Buffer is determined by
HI_CONTROL.EnVB. If the Vertex Buffer is used, indices are required to index the geometry data in the Vertex
Buffer. The required indices can be sent by CPU (index-transfer mode) or can be generated in the Host Interface
(auto-increment mode). There can be several indices in a DWORD from CPU depending on
HI_CONTROL.IdxType (data type of index). These transferred or generated indices are used in the following way.
1. Get a count from CPU
2. Get an index from CPU or previous index; // depending on HI_CONTROL.AutoInc. In Non-Index mode, 0xFFFFFFFF is used.
3. Add HI_IDXOFFSET.VALUE to the index for Index mode // In Non-Index mode, this step is skipped.
4. for each n from 0x0 to 0xF
5. if(HI_CONTROL.EnVB == 1 && HI_ATTRIB[n]_VBCTRL.Range != 0 && index < HI_ATTRIB[n]_VBCTRL.Range)
6. Use DWORDs fetched from
VertexBuffer[
HI_ATTRIB [ n ] _VBBASE . Addr + index * HI_ATTRIB [ n ] _VBCTRL . Stride ]; // Index mode
7. else
8. Fetch DWORDs from CPU and use them as the geometry data; // Non-Index mode
9. Transform DWORDs into floating point using HI_ATTRIB [ n ]. Dt and send them to vertex shader.
10. if ( HI_ATTRIB [ n ].LastAttrib == 1) break;
11. end for
12. repeat step 2~11 ( count ) times. // the ( count ) value in step 1 is used.
In step 8 and 9, the number of used DWORDs is determined by HI_ATTRIB n .Dt (data type of transferred
DWORD) and HI_ATTRIB n .NumComp (the number of components for each attribute). In step 8, the Host
Interface does not recognize what the DWORDs really are. The Host Interface only fetches the required number
of DWORDs from CPU. This is the reason why CPU must transfer indices and geometry data properly.
In step 9, HI_ATTRIB[n].Dt determines how the transferred DWORD is transformed into the floating point format.
(Normalization can be performed.) Also, in the same step, the order of components of each attribute can be
switched by SrcX~SrcW in each HI_ATTRIB
n . SrcX~SrcW is initialized as 0 value mapping first transferred data
to SrcX~SrcW. If (x, y, z, w) attribute is to be transferred in order, SrcW~SrcX must be set to the value 2’b11,
2’b10, 2’b01, 2’b00 respectively. This configuration is useful when color value is transferred in BGRA instead of
RGBA. If the number of each component is not four, then 0.0, 0.0, and 1.0 are automatically appended. For
example, if (x, y) data is transferred, then (FLOAT(x), FLOAT(y), 0.0, 1.0) is sent to the vertex shader.
Note that DWORDs transferred from CPU or in the Vertex Buffer for vertex attributes must be DWORD aligned . If
(8-bit x, 8-bit y, 8-bit z) is to be transferred, the last 8-bit data ([31:24] fields of the transferred DWORD) is ignored.
Note that HI_ATTRIB[n]_VBCTRL.Range must be set properly; the indices from CPU must be less than
HI_ATTRIB[n]_VBCTRL.Range.