Section 4 - Drawing Colors

8/14/2019 Section 4 - Drawing Colors

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Computer GraphicsComputer Graphics

Using Direct 3DUsing Direct 3D

Drawing & ColorsDrawing & Colors


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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 & Index Buffers

Color Representation

Shading

Rendering State

Moving to 3D


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Vertex Buffer

As mentioned before, the basicdrawing elements are vertices and

primitives. Vertices hold information such as

coordinates, colors and texture

coordinates while primitives are basicelements composed of thesevertices.


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Vertex Buffer (Cont.)

Vertex information is placed in avertex buffer.

What we need is to Create a vertex buffer

Fill it Use it to draw primitives


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To create a vertex buffer we mainlyneed to specify

The size of the buffer. What kind of information each vertex will

hold.


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FVF (Flexible Vertex Format) code isan 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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Example FVF Flags D3DFVF_DIFFUSE : Indicates the presence of a diffuse color

component

D3DFVF_XYZ : Indicates the presence of untransformedcoordinates

D3DFVF_XYZRHW : Indicates the presence of transformedcoordinates

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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The Usageparameter indicates how the bufferwill 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 toplace the buffer in the bast memory for writing.

We will set this parameter to 0 in most cases.


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The Poolparameter determines the memoryarea that will hold the buffer

D3D Resources can be placed in systemmemory, local video memory, AGP memory ...etc

Each has its pros & cons

We will use D3DPOOL_DEFAULTorD3DPOOL_MANAGED


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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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It is easier to deal with vertices asstructures rather than raw bytes.

This simplifies: Determining the size of the vertex usingsizeof(And hence the size of vertexbuffer)

Populating the vertex buffer


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Example: Transformed Lit Verticesstruct TransformedLitVertex

{

FLOAT x, y, z;

FLOAT rhw;

DWORD color;

};

#define FVF_TL (D3DFVF_XYZRHW | D3DFVF_DIFFUSE)


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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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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 ) ) ) { /*HandleFailure*/ }

//2. Write

memcpy( pVertices, vertices, sizeof(vertices) );//3. Unlock

VB->Unlock();


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Shading

Rendering State

Moving to 3D


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Drawing Primitives

Having prepared the vertex buffer itis 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


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Drawing Primitives (Cont.)

To draw a primitive we useDrawPrimitive method


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Some primitive types are D3DPT_POINTLIST

D3DPT_LINELIST D3DPT_LINESTRIP

D3DPT_TRIANGLELIST

D3DPT_TRIANGLESTRIP D3DPT_TRIANGLEFAN


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D3DPT_TRIANGLELIST


Image from MSDN


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D3DPT_TRIANGLELIST


Image from MSDN


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D3DPT_TRIANGLELIST

D3DPT_TRIANGLESTRIP D3DPT_TRIANGLEFAN Image from MSDN


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Drawing commands are issued betweenIDirect3DDevice9::BeginScene andIDirect3DDevice9::EndScene methods

ExampleDevice->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


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Think about it

Can you draw a cube using one drawingcommand 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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Shading

Rendering State

Moving to 3D


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Indexed Primitives

Indexed primitives are the solution to the problem ofredundant vertices

Instead of accessing the vertices in the vertex buffer instrict sequential order, provide an index array (called index

buffer) that specifies the order in which vertices in thevertex buffer are accessed. The point is that a vertex can bereferenced more than once in that array.

Image from alt.pluralsight.com


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Indexed Primitives (Cont.)

Index buffers are almost identical increation and usage to vertex buffers

D3DFMT_INDEX16

or D3DFMT_INDEX32 (Check device caps)

N * sizeof(WORD)

or N * sizeof(DWORD)

Depending on Format


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Index buffers are almost identical increation and usage to vertex buffers


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Just as we callIDirect3DDevice9::SetStreamSourceto the set the vertex buffer to be used, we

also callIdirect3DDevice9::SetIndices to setthe index buffer to be used


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To draw a primitive using a vertex buffer and anindex buffer, we useIDirect3DDevice9::DrawIndexedPrimitive


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Summing it up again



Create & Fill Index Buffer


Begin Scene

Set Stream Source Set Indices

Set FVF

Drawing Commands

End Scene

Present


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Shading

Rendering State

Moving to 3D


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A color is represented by an RGBtriplet. 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 thecorresponding D3DColor e.g.

D3DCOLOR red = D3DCOLOR_ARGB(255, 255, 0, 0)


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Direct3D9 provides D3DCOLORVALUE

A 128-bit color structure where eachcomponent is represented by a floating point(0 = no intensity, 1 = max intensity)


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Direct3D9 provides D3DXCOLOR

Similar to D3DCOLORVALUE but providesuseful constructors and overloaded operatorsfor e.g. (color addition and component-wisemultiplication)


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The color of a primitive by the colorof the vertices that constitute it.

To add color to vertices we add aD3DCOLOR (or DWORD) componentthe vertex structure and set theD3DFVF_DIFFUSE flag in the FVFcode.


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Note that you must use 32-bit colorrepresentation.

To use 128-bit color representationyou must use a custom vertex shader

(and of course there must be HWsupport).


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Shading

Rendering State

Moving to 3D


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Shading

Shading is the process of determiningthe colors of the pixels in a primitive

given the colors of vertices thatconstitute that primitive.


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Shading (Cont.)

The simplest shading technique is flatshading. Simply, the pixels in a

primitive get the color of the firstvertex in that primitive.

To use flat shading callDevice->SetRenderState(D3DRS_SHADEMODE, D3DSHADE_FLAT);


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Shading (Cont.)

The more elegant shading technique isGouraoud shading (a.k.a smooth

shading), where the color of a pixel islinearly interpolated using the colorsof all vertices in the primitive.


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Shading (Cont.)

Gouraud shading is the defaultshading technique in D3D.

If you enabled flat shading and wantto switch back to Gouraud shading,

callDevice->SetRenderState(D3DRS_SHADEMODE,D3DSHADE_GOURAUD);


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Shading (Cont.)

The following figure shows flat vs.Gouraud shading


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Color Representation Shading

Rendering State

Moving to 3D


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Rendering State

IDirect3DDevice9::SetRenderState is used to seta number of state variables that determine how D3Dwill 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 onlywhen needed. When set, they retain their new valuesuntil set again.


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Color Representation Shading

Rendering State

Moving to 3D


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Moving to 3D

Given the current D3D programstructure 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 verticesare untransformed.

Tell D3D how to map 3D vertexcoordinates to 2D screen coordinates

(specify transformation matrices).


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Moving to 3D (Cont.)

To enable the depth buffer, set the presentationparameters 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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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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To set a transformation we callDevice->SetTransformation(TransformationType,

TransformationMatrix)

The transformation matrix is apointer to a D3DMATRIX object


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Recall that we have three kinds oftransformations

World Transformation

Camera Transformation

Projection Transformation

So, TransformationType can beD3DTS_WORLD,D3DTS_VIEW or D3DTS_PROJECTION


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We do not need to fill the matrices by hand.Direct3D provides utility functions that creatematrices given the information we care about.

Examples of such functions are: D3DXMatrixTranslation, D3DXMatrixRotationX and

D3DXMatrixScaling for world transformation

D3DXLookAtRH for view transformation

D3DXMatrixPerspectiveLH for projectiontransformation

Details will be given in the lab


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Recall that transformations can be combinedby multiplying the corresponding matrices.


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Summing it up again



Create & Fill Index Buffer

Set Fixed Transformations


Begin Scene

Set Stream Source

Set Indices Set FVF

Set Frame-level/Object-level Transformations

Drawing Commands

End Scene

Present


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Any Questions ??

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Section 4 - Drawing Colors