Section 4 - Drawing Colors

Computer Graphics Using Direct 3D Drawing & Colors

Outline • Vertex Buffers • Drawing Primitives • Indexed Primitives & Index Buffers • Color Representation • Shading • Rendering State • Moving to 3D

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Outline

• Vertex Buffers • Drawing Primitives

• Indexed Primitives & Index Buffers • Color Representation • Shading • Rendering State • Moving to 3D

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Vertex Buffer • As mentioned before, the basic drawing elements are vertices and primitives. • Vertices hold information such as coordinates, colors and texture coordinates while primitives are basic elements composed of these vertices. 4

Vertex Buffer (Cont.) • Vertex information is placed in a vertex buffer. • What we need is to – Create a vertex buffer – Fill it – Use it to draw primitives 5

Vertex Buffer (Cont.) • To create a vertex buffer we mainly need to specify – The size of the buffer. – What kind of information each vertex will hold.

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Vertex Buffer (Cont.)

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Vertex Buffer (Cont.) • FVF (Flexible Vertex Format) code is an OR-Combination of flags that indicates – The information stored in each vertex – How the vertex will be processed by the fixed pipeline

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Vertex Buffer (Cont.) • Example FVF Flags – D3DFVF_DIFFUSE : Indicates the presence of a diffuse color component – D3DFVF_XYZ : Indicates the presence of untransformed coordinates – D3DFVF_XYZRHW : Indicates the presence of transformed coordinates – D3DFVF_NORMAL : Indicates the presence of normal vector component, which means the vertex is unlit – D3DFVF_TEX1 : Indicates the presence of texture coordinates for 1 texture

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Vertex Buffer (Cont.) • The Usage parameter indicates how the buffer will be used. For example: – D3DUSAGE_POINTS flag indicates that the buffer will be used to store point primitives. – D3DUSAGE_WRITEONLY indicates that the application will only write to the buffer. D3D tries to place the buffer in the bast memory for writing.

• We will set this parameter to 0 in most cases.

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Vertex Buffer (Cont.) • The Pool parameter determines the memory area that will hold the buffer • D3D Resources can be placed in system memory, local video memory, AGP memory ... etc • Each has its pros & cons • We will use D3DPOOL_DEFAULT or D3DPOOL_MANAGED

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Vertex Buffer (Cont.) • To fill the vertex buffer we – Lock it (and obtain memory address) – Fill the memory – Unlock it 0 Offset & Size = Lock the whole buffer You can set it to 0. Other values indicate intended usage to enhance performance

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Vertex Buffer (Cont.) • It is easier to deal with vertices as structures rather than raw bytes. This simplifies: – Determining the size of the vertex using sizeof (And hence the size of vertex buffer) – Populating the vertex buffer

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Vertex Buffer (Cont.) • Example: Transformed Lit Vertices struct TransformedLitVertex { FLOAT x, y, z; FLOAT rhw; DWORD color; }; #define FVF_TL (D3DFVF_XYZRHW | D3DFVF_DIFFUSE)

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Vertex Buffer (Cont.) • Example: Transformed Lit Vertices //Creating a vertex buffer IDirect3DVertexBuffer9* VB = NULL; if( FAILED(Device­>CreateVertexBuffer  ( 3*sizeof(TransformedLitVertex), 0 /*Usage*/,  FVF_TL, D3DPOOL_DEFAULT, &VB, NULL ) ) )     {         //Handle failure     }

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Vertex Buffer (Cont.) • Example: Transformed Lit Vertices //Filling the vertex buffer TransformedLitVertex vertices[] = { ... }; VOID* pVertices; //1. Lock and obtain address if( FAILED( VB­>Lock( 0, 0, (void**)&pVertices, 0 ) ) ) { /*Handle  Failure*/ } //2. Write memcpy( pVertices, vertices, sizeof(vertices) ); //3. Unlock VB­>Unlock();

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Outline

• Vertex Buffers • Drawing Primitives

• Indexed Primitives & Index Buffers • Color Representation • Shading • Rendering State • Moving to 3D

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Drawing Primitives • Having prepared the vertex buffer it is time to draw objects using the vertices in that buffer. • Before drawing we have to – Set the vertex buffer to read from – Set the FVF to assume 18

Drawing Primitives (Cont.) • To draw a primitive we use DrawPrimitive method

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Drawing Primitives (Cont.) • Some primitive types are – – – – – –

D3DPT_POINTLIST D3DPT_LINELIST D3DPT_LINESTRIP D3DPT_TRIANGLELIST D3DPT_TRIANGLESTRIP D3DPT_TRIANGLEFAN 20

Drawing Primitives (Cont.) • Some primitive types are – – – – – –

D3DPT_POINTLIST D3DPT_LINELIST D3DPT_LINESTRIP D3DPT_TRIANGLELIST D3DPT_TRIANGLESTRIP D3DPT_TRIANGLEFAN

Image from MSDN

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Drawing Primitives (Cont.) • Some primitive types are – – – – – –

D3DPT_POINTLIST D3DPT_LINELIST D3DPT_LINESTRIP D3DPT_TRIANGLELIST D3DPT_TRIANGLESTRIP D3DPT_TRIANGLEFAN

Image from MSDN

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Drawing Primitives (Cont.) • Some primitive types are – – – – – –

D3DPT_POINTLIST D3DPT_LINELIST D3DPT_LINESTRIP D3DPT_TRIANGLELIST D3DPT_TRIANGLESTRIP D3DPT_TRIANGLEFAN

Image from MSDN

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Drawing Primitives (Cont.) • Drawing commands are issued between IDirect3DDevice9::BeginScene and IDirect3DDevice9::EndScene methods • Example Device­>Clear(0, 0, D3DCLEAR_TARGET  , 0x0, 0, 0); Device­>BeginScene(); Device­>SetStreamSource( 0, VB, 0, sizeof(CUSTOMVERTEX) ); Device­>SetFVF( D3DFVF_CUSTOMVERTEX ); Device­>DrawPrimitive( D3DPT_TRIANGLELIST, 0, 2 ); Device­>EndScene(); Device­>Present(NULL,NULL,NULL,NULL);

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Summing it up • Setup

– Initialize D3D – Create & Fill Vertex Buffer

• Render – – – – – – –

Clear Buffers Begin Scene Set Stream Source Set FVF Drawing Commands End Scene Present 25

Think about it • Can you draw a cube using one drawing command without specifying a vertex in the buffer twice ?

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Think about it • Remember, redundant vertices = wasted memory BW + redundant vertex processing

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Outline

• Vertex Buffers • Drawing Primitives

• Indexed Primitives & Index Buffers • Color Representation • Shading • Rendering State • Moving to 3D

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Indexed Primitives • Indexed primitives are the solution to the problem of redundant vertices • Instead of accessing the vertices in the vertex buffer in strict sequential order, provide an index array (called index buffer) that specifies the order in which vertices in the vertex buffer are accessed. The point is that a vertex can be referenced more than once in that array.

Image from alt.pluralsight.com

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Indexed Primitives (Cont.) • Index buffers are almost identical in creation and usage to vertex buffers

N * sizeof(WORD) or N * sizeof(DWORD) Depending on Format

D3DFMT_INDEX16 or D3DFMT_INDEX32 (Check device caps)

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Indexed Primitives (Cont.) • Index buffers are almost identical in creation and usage to vertex buffers

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Indexed Primitives (Cont.) • Just as we call IDirect3DDevice9::SetStreamSource to the set the vertex buffer to be used, we also call Idirect3DDevice9::SetIndices to set the index buffer to be used

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Indexed Primitives (Cont.) • To draw a primitive using a vertex buffer and an index buffer, we use IDirect3DDevice9::DrawIndexedPrimitive

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Summing it up again • Setup

– Initialize D3D – Create & Fill Vertex Buffer – Create & Fill Index Buffer

• Render – – – – – – – –

Clear Buffers Begin Scene Set Stream Source Set Indices Set FVF Drawing Commands End Scene Present

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Outline

• Vertex Buffers • Drawing Primitives

• Indexed Primitives & Index Buffers • Color Representation • Shading • Rendering State • Moving to 3D

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Color Representation • A color is represented by an RGB triplet. Each component occupies a byte (0~255)

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Color Representation (Cont.) • Direct3D9 provides – D3DCOLOR type • An alias for DWORD

– D3DCOLOR_ARGB(a, r, g, b) macro • Accepts color components and returns the corresponding D3DColor e.g. D3DCOLOR red = D3DCOLOR_ARGB(255, 255, 0, 0)

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Color Representation (Cont.) • Direct3D9 provides – D3DCOLORVALUE • A 128-bit color structure where each component is represented by a floating point (0 = no intensity, 1 = max intensity)

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Color Representation (Cont.) • Direct3D9 provides – D3DXCOLOR • Similar to D3DCOLORVALUE but provides useful constructors and overloaded operators for e.g. (color addition and component-wise multiplication)

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Color Representation (Cont.) • The color of a primitive by the color of the vertices that constitute it. • To add color to vertices we add a D3DCOLOR (or DWORD) component the vertex structure and set the D3DFVF_DIFFUSE flag in the FVF code. 40

Color Representation (Cont.) • Note that you must use 32-bit color representation. • To use 128-bit color representation you must use a custom vertex shader (and of course there must be HW support). 41

Outline

• Vertex Buffers • Drawing Primitives

• Indexed Primitives & Index Buffers • Color Representation • Shading • Rendering State • Moving to 3D

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Shading • Shading is the process of determining the colors of the pixels in a primitive given the colors of vertices that constitute that primitive.

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Shading (Cont.) • The simplest shading technique is flat shading. Simply, the pixels in a primitive get the color of the first vertex in that primitive. • To use flat shading call Device­>SetRenderState(D3DRS_SHADEMODE, D3DSHADE_FLAT);

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Shading (Cont.) • The more elegant shading technique is Gouraoud shading (a.k.a smooth shading), where the color of a pixel is linearly interpolated using the colors of all vertices in the primitive.

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Shading (Cont.) • Gouraud shading is the default shading technique in D3D. • If you enabled flat shading and want to switch back to Gouraud shading, call Device­>SetRenderState(D3DRS_SHADEMODE,  D3DSHADE_GOURAUD);

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Shading (Cont.) • The following figure shows flat vs. Gouraud shading

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Outline

• Vertex Buffers • Drawing Primitives

• Indexed Primitives & Index Buffers • Color Representation • Shading • Rendering State • Moving to 3D

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Rendering State • IDirect3DDevice9::SetRenderState is used to set a number of state variables that determine how D3D will render the scene. • We saw the shading technique as an example. • In general Device­>SetRenderState(StateVariableName,  NewValue); • State variables have default values so you set them only when needed. When set, they retain their new values until set again. 49

Outline

• Vertex Buffers • Drawing Primitives

• Indexed Primitives & Index Buffers • Color Representation • Shading • Rendering State • Moving to 3D

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Moving to 3D • Given the current D3D program structure we developed. What do we need to draw 3D scenes ??

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Moving to 3D • We need to – Enable depth buffer. – Tell D3D that from now on, the vertices are untransformed. – Tell D3D how to map 3D vertex coordinates to 2D screen coordinates (specify transformation matrices).

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Moving to 3D (Cont.) • To enable the depth buffer, set the presentation parameters during initialization d3dpp.EnableAutoDepthStencil = true; d3dpp.AutoDepthStencilFormat = D3DFMT_D24S8;

• You have also to clear the depth buffer before rendering a new frame Device­>Clear(0, 0, D3DCLEAR_TARGET |  D3DCLEAR_ZBUFFER, 0xffffffff, 1.0f, 0);

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Moving to 3D (Cont.) • To indicate untransformed vertices – Remove rhw component from vertex structure. structure ColoredVertex { FLOAT x, y, z; D3DCOLOR color; };

– Use D3DFVF_XYZ flag instead of D3DFVF_XYZRHW in the FVF code. #define FVF_UTL (D3DFVF_XYZ | D3DFVF_DIFFUSE)

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Moving to 3D (Cont.) • To set a transformation we call Device­>SetTransformation(TransformationType,  TransformationMatrix)

• The transformation matrix is a pointer to a D3DMATRIX object

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Moving to 3D (Cont.) • Recall that we have three kinds of transformations

– World Transformation – Camera Transformation – Projection Transformation • So, TransformationType can be D3DTS_WORLD, D3DTS_VIEW or D3DTS_PROJECTION

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Moving to 3D (Cont.) • We do not need to fill the matrices by hand. Direct3D provides utility functions that create matrices given the information we care about. Examples of such functions are: – D3DXMatrixTranslation, D3DXMatrixRotationX and D3DXMatrixScaling for world transformation – D3DXLookAtRH for view transformation – D3DXMatrixPerspectiveLH for projection transformation

» Details will be given in the lab 57

Moving to 3D (Cont.) • Recall that transformations can be combined by multiplying the corresponding matrices.

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Summing it up again • Setup – – – –

Initialize D3D Create & Fill Vertex Buffer Create & Fill Index Buffer Set Fixed Transformations

– – – – – – – – –

Clear Buffers Begin Scene Set Stream Source Set Indices Set FVF Set Frame-level/Object-level Transformations Drawing Commands End Scene Present

• Render

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Any Questions ??

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