WebGL Simple 2D Example 11

Full JavaScript code on this page: (or you can View Page Source)

var gl, canvas, vertices = []

// Draws 2 triangles to make a rectangular image.
function drawImage(x, y, width, height, r, g, b, a, texX, texY, texWidth, texHeight) {
	var x2 = x+width
	var y2 = y+height
	var texX2 = texX + texWidth
	var texY2 = texY + texHeight
	vertices.push(
		x, y, r, g, b, a, texX, texY,
		x, y2, r, g, b, a, texX, texY2,
		x2, y2, r, g, b, a, texX2, texY2
	)
	vertices.push(
		x, y, r, g, b, a, texX, texY,
		x2, y, r, g, b, a, texX2, texY,
		x2, y2, r, g, b, a, texX2, texY2
	)
}

// UPDATE: Draw rectangle by drawing the white pixel in our PNG.
// The white pixel is near the top left of the PNG, at 1x1.
// The PNG is 128x128. Width is a percentage so pass 1/128 for 1px.
function drawRectangle(x, y, width, height, r, g, b, a) {
	drawImage(x, y, width, height, r, g, b, a, 1/128, 1/128, 1/128, 1/128)
}
	
function gameLoop() {
	window.requestAnimationFrame(gameLoop)
	
	// UPDATE: Draw a wide rectangle.
	drawRectangle(0,370, 200,50, 200,100,10,1)
	
	// Draw the moving image.
	var x = 250+Math.sin(Date.now()*.004)*250
	var y = 200
	var blue = 128 + Math.floor(Math.sin(Date.now()*.01) * 127)
	drawImage(
		x, y,
		100, 200,
		0, 255, blue, 1,
		0, .25, .25, .25
	)
	
	glRender()
}
	
function glRender() {
	// Clear the screen.
	gl.clear(gl.COLOR_BUFFER_BIT)

	// Tell webGL to draw these triangle this frame.
	gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW)

	// Draw all the triangles.
	gl.drawArrays(gl.TRIANGLES, 0, vertices.length/8)

	// Clear vertices. We will fill it every frame.
	// This way you don't need to delete objects from the screen. You just stop drawing them.
	vertices = []
}
	
function glSetup() {
	gl = myCanvas.getContext("experimental-webgl")

	// Set the background color to sky blue.
	gl.clearColor(.5, .7, 1, 1)

	// Tell webGL that we aren't doing anything special with the vertex buffer, just use a default one.
	gl.bindBuffer(gl.ARRAY_BUFFER, gl.createBuffer())

	// Vertex shader source code.
	var vertCode =
	"attribute vec2 coordinates;" +
	"attribute vec4 rgba;" +
	"attribute vec2 texPos;" +
	
	"varying highp vec4 rgbaForFrag;" +
	"varying highp vec2 texPosForFrag;" +
	"uniform vec2 canvasSize;" +
	
	"void main(void) {" +
		" vec2 drawPos;" +
		// Divide the position by our current canvas size.
		" drawPos = coordinates / canvasSize * 2.0;" +
		// We are passing in only 2D coordinates. Then Z is always 0.0 and the divisor is always 1.0
		" gl_Position = vec4(drawPos.x - 1.0, 1.0 - drawPos.y, 0.0, 1.0);" +
		// Pass the color and transparency to the fragment shader.
		" rgbaForFrag = vec4(rgba.xyz / 255.0, rgba.w);" +
		// Pass the texture position to the fragment shader.
		" texPosForFrag = texPos;" +
	"}"
	
	// Create a vertex shader object.
	var vertShader = gl.createShader(gl.VERTEX_SHADER)
	gl.shaderSource(vertShader, vertCode)
	gl.compileShader(vertShader)
	console.log(gl.getShaderInfoLog(vertShader))

	// Fragment shader source code.
	var fragCode =
	"varying highp vec4 rgbaForFrag;" +
	"varying highp vec2 texPosForFrag;" +
	"uniform sampler2D sampler;" +
	"void main(void) {" +
		" gl_FragColor = texture2D(sampler, texPosForFrag) * rgbaForFrag;" +
	"}"
	
	// Create fragment shader object.
	var fragShader = gl.createShader(gl.FRAGMENT_SHADER)
	gl.shaderSource(fragShader, fragCode)
	gl.compileShader(fragShader)
	console.log(gl.getShaderInfoLog(fragShader))

	// Tell webGL to use both my shaders.
	shaderProgram = gl.createProgram()
	gl.attachShader(shaderProgram, vertShader)
	gl.attachShader(shaderProgram, fragShader)
	gl.linkProgram(shaderProgram)
	gl.useProgram(shaderProgram)

	// Tell webGL to read 2 floats from the vertex array for each vertex
	// and store them in my vec2 shader variable I've named "coordinates"
	// We need to tell it that each vertex takes 32 bytes now (8 floats)
	var attribute = gl.getAttribLocation(shaderProgram, "coordinates")
	gl.vertexAttribPointer(attribute, 2, gl.FLOAT, false, 32, 0)
	gl.enableVertexAttribArray(attribute)

	// Tell webGL to read 4 floats from the vertex array for each vertex
	// and store them in my vec4 shader variable I've named "rgba"
	// Start after 8 bytes. (After the 2 floats for x and y)
	var attribute = gl.getAttribLocation(shaderProgram, "rgba")
	gl.vertexAttribPointer(attribute, 4, gl.FLOAT, false, 32, 8)
	gl.enableVertexAttribArray(attribute)

	// Tell webGL to read 2 floats from the vertex array for each vertex
	// and store them in my vec2 shader variable I've named "texPos"
	var attribute = gl.getAttribLocation(shaderProgram, "texPos")
	gl.vertexAttribPointer(attribute, 2, gl.FLOAT, false, 32, 24)
	gl.enableVertexAttribArray(attribute)
	
	// Tell webGL that when we set the opacity, it should be semi transparent above what was already drawn.
	gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA)
	gl.enable(gl.BLEND)
	
	var image = new Image()
	image.onload = function()
	{
		// Create a gl texture from our JS image object.
		gl.bindTexture(gl.TEXTURE_2D, gl.createTexture())
		gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, image)
		gl.activeTexture(gl.TEXTURE0)
		
		// Tell gl that when draw images scaled up, smooth it.
		gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR)
		gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR)
	}
	image.src = "tiles.png"
	
	// Call onresize to set the initial canvas size.
	window.onresize()
}

window.onresize = function() {
	// To test we'll make the canvas be 1/3 the browser width. Try resizing your browser.
	var width = Math.floor(innerWidth/3)
	var height = 500
	myCanvas.style.width = width+"px"
	myCanvas.style.height = height+"px"
	myCanvas.setAttribute("width", width)
	myCanvas.setAttribute("height", height)
	
	// Set the viewport size to be the whole canvas.
	gl.viewport(0, 0, width, height)
	// Set our shader variable for canvas size. It's a vec2 that holds both width and height.
	gl.uniform2f(gl.getUniformLocation(shaderProgram, "canvasSize"), width, height)
	
}

window.onload = function() {
	glSetup()
	gameLoop()
}