Assignment 3

Tema 3 - Canvas Painting with Compute Shader

Description

Implement a simple canvas painting tool using Compute Shader.

Resources

• Canvas Painting DEMO
  • keys: 0-9 (brush color)
  • Key - (eraser brush)
  • Key [ and ] - control brush radius
  • Keypad 0-9 (control brush opacity - not mandatory)
  • Key S saves the current canvas painting to local file awesome.png

Deadline

• 20 Ianuarie 2019 23:59 (soft deadline)
• After the soft deadline, penalty is 10 pct/per day up to a maximum of 50% (100 pct)

Tasks

Setup

• Disable window vsync

window->SetVSync(false); // in Init()

• Create 2 RGBA (8 bits per pixel) textures [10 pct]
  • 1 texture for keeping the resulting canvas painting
  • 1 texture for layer painting
  • you can ignore window resizing (as in the Demo)

auto resolution = window->GetResolution();
texture = new Texture2D();
texture->Create(nullptr, resolution.x, resolution.y, 4);

• Render the canvas texture as a full-screen texture [10 pct]
  • make sure that the window resolution perfectly matches the texture resolution
  • as long as the textures are created with the default window resolution it should
• Default canvas color should be white [rgb(1, 1, 1)] [5 pct]
• README: [5 pct]

Painting

• Draw brush position (and radius) [10 pct]
• Add support for simple brush painting (steps below) [80 pct]
• Add support for brush radius [30 pct]
  • default brush radius is 5px
  • add keys for increasing and decreasing brush radius with stepping of 1 pixel
  • grading is considered only if brush painting works
• Clear the canvas using a compute shader when key N is pressed [20 pct]
• Real-time feedback: Render the layer texture over the canvas texture during the painting operation [20 pct]
• Add support for the following 10 brush colors using the keyboard alpha-numeric keys [10 pct]

	if (key == GLFW_KEY_1) brushColor = glm::vec4(1, 0, 0, 1);	// red
	if (key == GLFW_KEY_2) brushColor = glm::vec4(1, 0.5, 0, 1);	// orange
	if (key == GLFW_KEY_3) brushColor = glm::vec4(1, 1, 0, 1);	// yellow
	if (key == GLFW_KEY_4) brushColor = glm::vec4(0, 1, 0, 1);	// green
	if (key == GLFW_KEY_5) brushColor = glm::vec4(0, 1, 1, 1);	// cyan
	if (key == GLFW_KEY_6) brushColor = glm::vec4(0, 0.5, 1, 1);	// light blue
	if (key == GLFW_KEY_7) brushColor = glm::vec4(0, 0, 1, 1);	// blue
	if (key == GLFW_KEY_8) brushColor = glm::vec4(0.5, 0, 1, 1);	// purple
	if (key == GLFW_KEY_9) brushColor = glm::vec4(1, 0, 1, 1);	// magenta
	if (key == GLFW_KEY_0) brushColor = glm::vec4(0, 0, 0, 1);	// white (erase)

Brush painting steps

• painting starts when left click is pressed OnMouseBtnPress
• While the mouse button is held down the layer textures must be updated with the paint area created by mouse movements [60 pct]
  • since mouse input is registered less frequently than the real movement the brush painting has to be interpolated
  • each frame
    • send to the compute shader the previous mouse position and the current mouse position
    • paint a line between the 2 points (with the specified line radius)
    • Point to line equation (In demo a variation of the cross product method is used)
      • from each compute thread (pixel) the distance to the line must be computed in order to decide if the pixel will be painted or not
• painting finished when the user release the left click OnMouseBtnRelease
• Using a compute shader copy the layer texture into the canvas texture [20 pct]

Total: 200 pct

Bonuses

• Optimize canvas brush painting by computing an AABB between the mouse position (current and previous) and do an early return for the compute threads that are outside of it
• Implement a simple clone-stamp tool
  • use shift to position a
  • copy from canvas texture in the layer texture
  • after mouse release
• Add brush opacity like in the demo
  • layer combination can be done like this (in demo is the)

canvasColor.rgb = layerColor.rgb * layerColor.a + canvasColor.rgb * (1 - layerColor.a);

Project Archive

• make sure you don't include temporary compiled files in the archive
  • right of Solution Explorer → Clean Solution
  • delete /Visual Studio/obj and /Visual Studio/.vs folder
• the archive should only contain
  • /Visual Studio
  • /Source
  • /Resources
  • /libs
  • README.txt - readme for the assignment