Ejemplo n.º 1
0
func onPaint(sz size.Event) {
	gl.ClearColor(1, 0, 0, 1)
	gl.Clear(gl.COLOR_BUFFER_BIT)

	gl.UseProgram(program)

	green += 0.01
	if green > 1 {
		green = 0
	}
	gl.Uniform4f(color, 0, green, 0, 1)

	gl.Uniform2f(offset, touchX/float32(sz.WidthPx), touchY/float32(sz.HeightPx))

	gl.BindBuffer(gl.ARRAY_BUFFER, buf)
	gl.EnableVertexAttribArray(position)
	gl.VertexAttribPointer(position, coordsPerVertex, gl.FLOAT, false, 0, 0)
	gl.DrawArrays(gl.TRIANGLES, 0, vertexCount)
	gl.DisableVertexAttribArray(position)

	debug.DrawFPS(sz)
}
Ejemplo n.º 2
0
// Draw draws the srcBounds part of the image onto a parallelogram, defined by
// three of its corners, in the current GL framebuffer.
func (img *Image) Draw(sz size.Event, topLeft, topRight, bottomLeft geom.Point, srcBounds image.Rectangle) {
	// TODO(crawshaw): Adjust viewport for the top bar on android?
	gl.UseProgram(glimage.program)
	tex := texmap.get(*img.key)
	if tex.needsUpload {
		img.Upload()
		tex.needsUpload = false
	}

	{
		// We are drawing a parallelogram PQRS, defined by three of its
		// corners, onto the entire GL framebuffer ABCD. The two quads may
		// actually be equal, but in the general case, PQRS can be smaller,
		// and PQRS is not necessarily axis-aligned.
		//
		//	A +---------------+ B
		//	  |  P +-----+ Q  |
		//	  |    |     |    |
		//	  |  S +-----+ R  |
		//	D +---------------+ C
		//
		// There are two co-ordinate spaces: geom space and framebuffer space.
		// In geom space, the ABCD rectangle is:
		//
		//	(0, 0)           (geom.Width, 0)
		//	(0, geom.Height) (geom.Width, geom.Height)
		//
		// and the PQRS quad is:
		//
		//	(topLeft.X,    topLeft.Y)    (topRight.X, topRight.Y)
		//	(bottomLeft.X, bottomLeft.Y) (implicit,   implicit)
		//
		// In framebuffer space, the ABCD rectangle is:
		//
		//	(-1, +1) (+1, +1)
		//	(-1, -1) (+1, -1)
		//
		// First of all, convert from geom space to framebuffer space. For
		// later convenience, we divide everything by 2 here: px2 is half of
		// the P.X co-ordinate (in framebuffer space).
		px2 := -0.5 + float32(topLeft.X/sz.WidthPt)
		py2 := +0.5 - float32(topLeft.Y/sz.HeightPt)
		qx2 := -0.5 + float32(topRight.X/sz.WidthPt)
		qy2 := +0.5 - float32(topRight.Y/sz.HeightPt)
		sx2 := -0.5 + float32(bottomLeft.X/sz.WidthPt)
		sy2 := +0.5 - float32(bottomLeft.Y/sz.HeightPt)
		// Next, solve for the affine transformation matrix
		//	    [ a00 a01 a02 ]
		//	a = [ a10 a11 a12 ]
		//	    [   0   0   1 ]
		// that maps A to P:
		//	a × [ -1 +1 1 ]' = [ 2*px2 2*py2 1 ]'
		// and likewise maps B to Q and D to S. Solving those three constraints
		// implies that C maps to R, since affine transformations keep parallel
		// lines parallel. This gives 6 equations in 6 unknowns:
		//	-a00 + a01 + a02 = 2*px2
		//	-a10 + a11 + a12 = 2*py2
		//	+a00 + a01 + a02 = 2*qx2
		//	+a10 + a11 + a12 = 2*qy2
		//	-a00 - a01 + a02 = 2*sx2
		//	-a10 - a11 + a12 = 2*sy2
		// which gives:
		//	a00 = (2*qx2 - 2*px2) / 2 = qx2 - px2
		// and similarly for the other elements of a.
		writeAffine(glimage.mvp, &f32.Affine{{
			qx2 - px2,
			px2 - sx2,
			qx2 + sx2,
		}, {
			qy2 - py2,
			py2 - sy2,
			qy2 + sy2,
		}})
	}

	{
		// Mapping texture co-ordinates is similar, except that in texture
		// space, the ABCD rectangle is:
		//
		//	(0,0) (1,0)
		//	(0,1) (1,1)
		//
		// and the PQRS quad is always axis-aligned. First of all, convert
		// from pixel space to texture space.
		w := float32(tex.width)
		h := float32(tex.height)
		px := float32(srcBounds.Min.X-img.RGBA.Rect.Min.X) / w
		py := float32(srcBounds.Min.Y-img.RGBA.Rect.Min.Y) / h
		qx := float32(srcBounds.Max.X-img.RGBA.Rect.Min.X) / w
		sy := float32(srcBounds.Max.Y-img.RGBA.Rect.Min.Y) / h
		// Due to axis alignment, qy = py and sx = px.
		//
		// The simultaneous equations are:
		//	  0 +   0 + a02 = px
		//	  0 +   0 + a12 = py
		//	a00 +   0 + a02 = qx
		//	a10 +   0 + a12 = qy = py
		//	  0 + a01 + a02 = sx = px
		//	  0 + a11 + a12 = sy
		writeAffine(glimage.uvp, &f32.Affine{{
			qx - px,
			0,
			px,
		}, {
			0,
			sy - py,
			py,
		}})
	}

	gl.ActiveTexture(gl.TEXTURE0)
	gl.BindTexture(gl.TEXTURE_2D, tex.gltex)
	gl.Uniform1i(glimage.textureSample, 0)

	gl.BindBuffer(gl.ARRAY_BUFFER, glimage.quadXY)
	gl.EnableVertexAttribArray(glimage.pos)
	gl.VertexAttribPointer(glimage.pos, 2, gl.FLOAT, false, 0, 0)

	gl.BindBuffer(gl.ARRAY_BUFFER, glimage.quadUV)
	gl.EnableVertexAttribArray(glimage.inUV)
	gl.VertexAttribPointer(glimage.inUV, 2, gl.FLOAT, false, 0, 0)

	gl.DrawArrays(gl.TRIANGLE_STRIP, 0, 4)

	gl.DisableVertexAttribArray(glimage.pos)
	gl.DisableVertexAttribArray(glimage.inUV)
}