I'm a begginer in DirectX programming and Im currently trying to draw a simple triangle to the screen using world, view and projection matrices. I have a feeling i'm calculating the matrices wrong as the triangle dosn't appear on the screen, but if i set all the matricies to the identity matrix then the triangle appears ( with no transformations obviously ).

Whats the best way to get help with this issue, do i upload my project? or should i run through the calculation process with the values i use and see if anyone spots something blatantly wrong?

Thank you.

You can skip all transformation matrices if you want to draw to the screen space. With D3D 11 for example, you can use vertex shader as pass-through without transforming. You'll just need some scaling and adding since the view space ranges from (-1.0,-1.0) to (1.0,1.0). So that means that you'll divide the x position with half of the back buffer width and subtract 1.0f. And same for the y position component.

Cheers!

Thanks Jason. Im using the DirectXMath variables and functions. I'm not sure where to add those flags, but i do use XMMatrixTranspose(); on each matrix before i set them to the constant buffer, which i think does the same thing. I've tried with and without transposing the matrices. Im almost certain the problem is the projection matrix. I'll show the calculations, see what you think.

This is the three vertices of the triangle.

{ XMFLOAT3( -1.0f, -1.0f, 0.0f ) },
{ XMFLOAT3( +0.0f, +1.0f, 0.0f ) },
{ XMFLOAT3( +1.0f, -1.0f, 0.0f ) }

The view matrix: ( Rotation is zero so it can be ignored. )

XMFLOAT3 up, position, lookAt;
XMVECTOR vUp, vPosition, vLookAt;
float yaw, pitch, roll;
XMMATRIX rotationMatrix;

// Set the vector that points upwards.
up.x = 0.0f;
up.y = 1.0f;
up.z = 0.0f;
vUp = XMLoadFloat3( &up );

// Set the position of the camera in the world.
position.x = 0.0f;
position.y = 0.0f;
position.z = -10.0f;
vPosition = XMLoadFloat3( &position );

// Set where the camera is looking at by default.
lookAt.x = 0.0f;
lookAt.y = 0.0f;
lookAt.z = 1.0f;
vLookAt = XMLoadFloat3( &lookAt);

// Convert the rotation angles to radians. ( these are all 0, no rotation )
pitch = XMConvertToRadians( m_rotationX ); 
yaw   = XMConvertToRadians( m_rotationY );
roll  = XMConvertToRadians( m_rotationZ );

// Create the rotation matix based on the Yaw Pitch Roll. ( again this comes out as an identity matrix, no rotation )
rotationMatrix = XMMatrixRotationRollPitchYaw( pitch, yaw, roll );

// Transform the "lookAt" and "up" vectors to rotate the camera at its origin.
vUp = XMVector3TransformCoord( vUp, rotationMatrix );
vLookAt = XMVector3TransformCoord( vLookAt, rotationMatrix );

// Translate the rotated camera position to the position of the viewer.
vLookAt = vPosition + vLookAt;

// Finaly create the view matrix from the three updated vectors.
m_viewMatrix = XMMatrixLookAtLH( vPosition, vLookAt, vUp );

The world matrix is just set as an identity matrix, the triangle is at the origin of the world.

m_worldMatrix = XMMatrixIdentity();

The projection matrix:

screenWidth = 800;
screenHeight = 600;
screenNear = 0.1f;
screenDepth = 1000.0f;

float fieldOfView = (float)XM_PI / 4.0f;
float screenAspect = (float)screenWidth / (float)screenHeight;

m_projectionMatrix = DirectX::XMMatrixPerspectiveFovLH( fieldOfView, screenAspect, screenNear, screenDepth );

Transpose the matrices and set them to the constant buffer:

// Transpose the matrices to prepare them for the shader.
XMMatrixTranspose( worldMatrix );
XMMatrixTranspose( viewMatrix );
XMMatrixTranspose( projectionMatrix );

// Lock the constant buffer so it can be writen to.
deviceContext->Map( m_matrixBuffer, 0, D3D11_MAP_WRITE_DISCARD, 0, &mappedResource );


// Get a pointer to the data in the constant buffer.
dataPtr = (MatrixBufferType*)mappedResource.pData;

// Copy the matrices into the constant buffer.
dataPtr->world = worldMatrix;
dataPtr->view = viewMatrix;
dataPtr->projection = projectionMatrix;

// Unlock the constant buffer.
deviceContext->Unmap( m_matrixBuffer, 0 );

// Set the constant buffer in the vertex shader with the updated values.
deviceContext->VSSetConstantBuffers( 0, 1, &m_matrixBuffer );

The think final vertices positions comes out as this.

{-1.81066000, -2.41421342, 9.90099049, 10.0000000}
{0.000000000, 2.41421342, 9.90099049, 10.0000000}
{1.81066000, -2.41421342, 9.90099049, 10.0000000}

The vertices should be visible? Thats even more puzzling. I've tryed swapping vertices and i've even set the raster state to D3D11_CULL_NONE so i can see both sides, still nothing. Apparently in the latest Windows SDK, PIX is replaced by the Gaphics Debugger which is only available in the retail version of Visual Studio, im using the Express version so thats a pain.

Like i say, if i dont use the matrices, or even set them to be Identity matrices, then the triangle appears as expected.

Wish i could se what the values in the shader are at run time. This is what my shaders look like.

// Constant Buffer---------------------------------------------------------------

cbuffer MatrixBuffer
{
	matrix worldMatrix;
	matrix viewMatrix;
	matrix projectionMatrix;
};

// Type defines-----------------------------------------------------------------

struct VSInput
{
	float4 position : POSITION;
	float4 color	: COLOR;
};

struct PSInput
{
	float4 position : SV_POSITION;
	float4 color	: COLOR;
};

// Vertex Shader---------------------------------------------------------------

PSInput VS( VSInput input )
{
	PSInput output;

	// Change the position to be 4 units for proper matrix calculations.
	input.position.w = 1.0f;

	// Calculate the position of the vertex against the world, view and projection matrices.
	output.position = mul( input.position, worldMatrix );
	output.position = mul( output.position, viewMatrix );
	output.position = mul( output.position, projectionMatrix );

	// Store the color.
	output.color = input.color;

	return output;
}

// Pixel Shader-------------------------------------------------------------------

float4 PS( PSInput input ) : SV_TARGET
{
    return input.color;
}

Like i said, i've tried that and the triangle appears fine. Which is why i'm pretty confident its the matrix calculations that are wrong, specifically the projection matrix.

If i add just this line to the code, the triangle appears.

projectionMatrix = XMMatrixIdentity();

I found out that the retail version of Visual Studio has a ninty day trial. Im'a go download that, figure out how to use the Graphics Debugger and see what the values are in the shader. Thanks for your help so far, really appreciate it.

XMMatrixTranspose( worldMatrix );
XMMatrixTranspose( viewMatrix );
XMMatrixTranspose( projectionMatrix );

worldMatrix = XMMatrixTranspose( worldMatrix );
viewMatrix = XMMatrixTranspose( viewMatrix );
projectionMatrix = XMMatrixTranspose( projectionMatrix );

Haha that was it! I didnt store the returned values when i transposed them. Thank so much! *facepalm*